There are a number of symbols in The Merry Adventures of Robin Hood, but I'll discuss three that are important in the cultural context of the work.
Two of the most important symbols in the work are expressed in the setting in which the adventures take place. In the Robin Hood myth, one of the symbols most important to the story--the forest--is also culturally significant in English literature:
And here is a country bearing a well-known name, wherein no chill mists press upon our spirits, and no rain falls but what rolls off our backs like April showers. . . where flowers bloom forever and birds are always singing. . . and ale and beer. . . flow like water in a brook.
The world that protects Robin and the Merry Men from harm is essentially a paradise, part of the world going back to the Golden Age where men were free from the political and societal evils represented by men such as the Sheriff of Nottingham and the usurper, King John. In other words, the forest symbolizes both a place and time in which men were free to live and pursue their happiness. And the opposite of this symbol of the Golden Age is the town of Nottingham, along with its sheriff, where freedom is curtailed and danger is everywhere in the form of corrupt political power. One of the general themes we see in English literature is the conflict between the natural life, usually represented by the forest, and city life, in this case represented by Nottingham.
During the episode in which Robin fights Little John at the stream crossing, we are told that "never did the Knight's of Arthur's Round Table meet in a stouter fight than did these two." This is, of course, an allusion to the golden age of Arthur and his knights, but it is also an effective symbol of the glory and chivalry that characterized the time of Arthur, who was also, like Robin Hood, a defender of the weakest members of society.
Symbols also appear in the clothes worn by Robin and the Merry Men and the Sheriff. For example, Robin and his followers are generally described as wearing "Lincoln green, and a fine show they made, seated upon the sward beneath that fair, spreading tree." Lincoln green is, therefore, symbolic of the life of the forest and is always identified with men who protect those who have no other protection against the inroads of the corrupt political and economic power of the Sheriff, who is described as wearing
. . . a purple velvet cap, and purple velvet was his robe, all trimmed about with rich ermine; his jerkin and hose were of sea-green silk. . . .
Purple was the color of royalty, aristocracy, and power; in fact, in many cultures, including English society, purple was restricted to the use of the aristocracy, and common people were not even allowed to wear garments of that color. For the majority of the people in Robin's world, purple symbolized all of the negative attributes of an aristocracy--burdensome taxes, enforced military service, a general lack of freedom.