For the most part, the meaning of the symbols in The Glass Menagerie don't change they consistently reflect the conditions in which the characters live, such as Laura's fragile nature which is symbolically illustrated through the glass menagerie. The only element of this symbol that changes is the unicorn.
The glass unicorn is a symbol for Laura, who is not like the other horses in her collection because the horn on his head makes him a little bit different. Like Laura, who is not like other girls, because she has a slight limp. But after Laura's romantic interlude with Jim O'Connor, and while dancing, they accidentally knock the unicorn off the table and the horn breaks off, Laura is changed into a regular girl at the same time that the unicorn is changed into a regular horse.
The only changing symbol in the play is the unicorn.
The need for true escape from the torment and confinement that exists within the walls of the apartment as symbolically represented in the fire escape, and Mr. Wingfield's picture that hangs in the apartment remain constant. Tom longs for escape, resenting and admiring his father at the same time, one for getting out of the relationship with his mother and two for abandoning him.
Tom steps out onto the fire escape frequently foreshadowing his future escape from the frustrations that exist in the apartment and his following in his father's footsteps.
Amanda's most powerful symbol in the play is her past, her memory of her girlhood in the Blue Mountains where she was so popular that 17 gentleman callers arrived one Sunday afternoon. Amanda's memories will remain with her and there is no way for the reader to know if they are true or exaggerated.
One of the most powerful themes in the play is illusion versus reality, it is hard to establish what is real within the Wingfield's world other than the obvious.