The question is very unclear with respect to the version or edition of Tennessee Williams' 1945 play The Glass Menagerie. What follows, therefore, is an attempt at responding to the student's question in a broader sense, but with reference to different program or "Playbill" covers that accompanied productions of the play from its infancy to the present.
Williams' play deals with a troubled, somewhat dysfunctional family of three: Amanda Wingfield, her grown son Tom, and her daughter Laura. The latter is a physically-handicapped young woman whose sheltered, almost agoraphobic existence is characterized by her immersion in an imaginary world consisting of her collection of small glass figurines, all in the shape of animals. Laura's collection of glass figurines, the "glass menagerie" of the title, represents her own delicate status. As Williams himself wrote in his production notes accompanying his play:
"A childhood illness has left her crippled, one leg slightly shorter than the other, and held in a brace. . .Stemming from this, Laura's separation increases till she is like a piece of her own glass collection, too exquisitely fragile to move from the shelf."
The aforementioned program covers, then, depict glass figurines in the shape of animals. One particular program cover, though, shows only a unicorn, a special addition to Laura's glass menagerie that is accidentally broken during her one chance at emotional fulfillment when she dances with Jim O'Conner, the somewhat dull young man brought home by Tom in the hopes that Jim and Laura will spark a romance. Unicorns, of course, symbolize purity and innocence, which are two defining characteristics of Laura Wingfield. The accident that results in the glass unicorn's horn being broken off symbolizes the end of the Wingfield family's hopes for a better future in which Laura is able to break free of the emotional restraints that confine her to the family's apartment and lead a more normal life.
The probable answer to the student's question, then, is that the glass figurines are animals and/or a depiction of a unicorn.