person's beliefs and actions were subject to criticism. 

Young Goodman Brown tells the devil in the forest that he was held back by "Faith"  when he comes to the meeting late. Obviously, Brown's statement refers to his wife Faith. The devil perceives that Brown, because of his religious faith, hesitated to meet with him and carry through with the plans [probably a sell your soul idea] that Hawthorne does not actually state in the story.  

The description of Faith Brown includes her pink ribbons.  The color pink has symbolically stood for innocence.   To Goodman Brown, his wife represented everything pure and good. Ribbons also imply a carefree spirit. 

 “With heaven above and Faith below, I will yet stand firm against the devil!” cried Goodman Brown.

When Goodman Brown sees the pink ribbon in the forest, he loses his faith both literally and figuratively.  

There was a scream...But something fluttered lightly down through the air and caught on the branch of a tree. The young man seized it, and beheld a pink ribbon.

“My Faith is gone!” cried he...“There is no good on earth; and sin is but a name."

Hawthorne used the ribbon to subtly reinforce the idea that Faith was a part of the satanic ritual.  This powerful symbol led Goodman Brown to divorce himself spiritual, emotionally, and physically from the rest of the townspeople.  Despite the fact that he remained with Faith and they had children, he was no longer the husband or man that Faith watched go into the forest. 

The ambiguity of the story centers on the reality of the events.  Did Goodman Brown dream or actually experience the meeting with the devil and seeing the other townspeople that he had respected? Hawthorne cleverly leaves the reader with many questions about the woodland happenings.  When Goodman Brown returns to town a bitter man, his wife has the same pink ribbons in her hair as before. Faith, at least to the outside world, maintains her innocent heart. 

Since Brown was so dependent on Faith for his religious grounding, he loses everything when he discovers the ribbons in the wood. This is the turning point for him.  He will never trust anyone again because the most important person in his life left him with doubt in his heart. That is the significance of the ribbons. 

The ribbons are symbols of Faith's purity and youth. They are decorations that a young, pure, faithful wife can reasonably wear, even in Puritan society, and not be considered vain. Hawthorne mentions them so many times to enforce the idea of Faith's purity. As Young Goodman Brown leaves her, he can still see her ribbons blowing in the wind, and he is reminded, once again of her purity.

Later, he recognizes Faith in the forest at the witches' coven meeting, and she has her pink ribbons again, but this time they fall out of her hair, indicating that she has lost her innocence and purity. This represents the final catastrophe to Young Goodman Brown, who has already seen his father and several other supposedly upstanding, righteous people consorting with the devil. And now, he sees his once pure and innocent wife.

Interestingly and mysteriously, though, when Young Goodman Brown returns home at the end of the story, there is Faith, and she still has the ribbons! So-- did he imagine everything? Is she still pure and innocent? That is the intrigue of the story.

The most common answer to your question is that the pink hair ribbons symboize Faith's innocence and when she loses it so that Brown finds them on the ground it signifies her loss of innocence.  But I wonder if the symbolism is as simple as that.  Pink hair ribbons would have been frowned upon if allowed at all in the austere of Puritan New England.  Most women, married or unmarried would have covered their hair with a cap.  So here goes my explanation which may or may not be right.

I believe that one of the theme's of Hawthorne's story is that there is sin in all of us no matter how pious we are on the outside.  This is what Brown realizes in his trip (or dream) to visit the devil.  Even though these people have claimed salvation, Satan still rules their flesh.  Thus the pink ribbons rather than symbolizing purity (they would have been white if that were the case), symbolize the mixture of good and evil (with white for good and the red of Satan for evil) in all of us, including Faith. They, I think, also symbolized the uncertainty of Brown's faith so that when he found them on the ground they represented his loss of faith, and Faith's apparent abandoment of the good half of her for the pure evil of Satan.  The fact that the ribbons are in Faith's hair upon his return would signify that she rejected Satan's total controll and signify Brown's still mixed faith.

We associate the pink ribbons with Faith, Goodman Brown's young wife, whose innocence and devout character are seemed to be represented in part by the colour of her ribbons. I think potentially that the falling to the ground of these ribbons can symbolise one of the themes of the story, which is the fact that we are all sinners - none of us are so good as to avoid the taint of sin on our lives entirely. It is clear that at the beginning of the story Goodman Brown idolises his wife, and yet the 'dream' he has in the forest causes him to doubt his impressions of her. It is this 'fall' from the pedestal that he has put her on that is symbolised by the fall of the ribbons.

Don't forget though that pink is not pure innocence such as the color white would suggest.  Pink is created by mixing white with red.  Red has symbolic associations with blood, love, passion, evil, fire, etc.  While red can have both positive and negative suggestions, the red fire and the evil of the devil are clearly brought up in this story, and Faith's pink ribbons are found, and abondoned at the witch meeting in the dark forest.  Whatever innocence they may have represented is lost, and they never represented pure innocence at all.  Faith is tempted and fearful at the start of the story and wants Brown to stay with her, perhaps to keep her from the temptation he thinks is only his challenge.

Pink is a color that is symbolic of innocence and naivete.  In Hawthorne's "Young Goodman Brown," the pink ribbons that Faith wears at the beginning of the narrative represent the ingenuousness of Brown, who does not understand the terrible significance of the journey upon which he embarks with the old man. 

As he is in the forest and witnesses the Black Sabbath, Brown sees the pink ribbons of Faith fall to the ground, indicating Brown's personal loss of faith. 

It is also important to consider Faith's context -- the wearing of pink ribbons by a Puritan woman (who dressed very conservatively and avoided bright color) may be seen as an expression of joyful innocence or the budding sexuality of a young wife (remember, she wants him to sleep beside her, and she can barely restrain herself from kissing him in the street), but it may also be seen as an indication that she is not a "good" Puritan, and thus serve to foreshadow her later presence at the Black Mass.

Brown believes that because Faith is elected to Heaven, he will be as well -- and when he sees her ribbons in the forest, that belief crumbles.

The pink ribbon belonging to Young Goodman Brown's wife, Faith, is an outward symbol of her presence at the meeting in the woods.  The last time he saw her hair ribbons, she was sweetly kissing him goodbye before he left for his journey into the forest.  He knew that he was off to meet with the devil, and that he was embarking on an evening of evil.  Goodman Brown kept telling himself that after this one evening he was going to live a life of goodness with Faith.  When he sees her at the meeting, he believes that his Faith is lost (both his wife is lost to evil and his personal faith in goodness has been destroyed).  The ribbon floating in the air is a physical reminder that she was there at the devil's meeting in the woods.  He is reminded of her presence at the meeting when he returns home to find her wearing the pink ribbons.

Initially when Brown leaves his wife and her pink ribbons behind, they represent innocence.  For when he leaves for the wilderness he is a much different man than when he returns.  Brown's faith in his religion, town, wife, and destiny are firm.  However, once he meets the devil in the wilderness, all those change.  Finally, when he thinks he hears her voice in the woods and sees her ribbon descend from above, he cries, "My Faith is gone."  Of course, his faith in all that he held dear - his religion, town, wife, and destiny is gone.  Seeing that ribbon in the wilderness causes Brown to literally lose his faith and his innocence.  Notice that now as he tears through the woods with the devil's second staff (Goody Cloyse took the first), Hawthorne observes that nothing in the wilderness - not the black mass nor the devil himself - was as frightening as Goodman Brown. 

I think that the pink ribbons are a link between the conception of Faith as good and as evil.  If Faith were purely good, her hair ribbons would have been white not pink.  Indeed, pink was not an approved color in the Puritan society in which she lived.  They wore somber clothes usually in dark colors.  Thus I believe that the pink ribbons are a mixture of red for the evil of Satan, and the white of purity, thus combining the presentation of Faith as the virtuous wife waiting for her husband and the presentation of Faith as the evil harlot of Satan. 

This is a difficult response for “Faith” is very ambiguous in the story, carrying more than two meanings.  The ribbons are mentioned in conjunction with Faith when we meet her “thrust[ing] her own pretty head into the street, letting the wind play with the pink ribbons of her cap.” Her ribbons are mentioned two more times immediately: “Faith with the pink ribbons” blesses him as he leaves, and he looks back to see “Faith still peeping after him, with a melancholy air, in spite of her pink ribbons, causing him to think “Poor little Faith.” Putting these introductory passages together, faith can be bold, sufficient unto itself so that it can play “in the wind” and retain itself; faith can be good and trusting, which we see when Faith blesses Brown, and finally faith can be sad because it is not sufficiently strong to withstand adversity (“poor little Faith”).  It is this final aspect of faith that the story leaves us with at its conclusion, for Brown’s faith was insufficient to trust in his wife and his neighbors, insufficient to allow him to retain a sense of humanity even if its sometimes marred by evil and guilt.