Not a joke. Here's the description from Christies:
A ROMAN GLASS GAMING DIE
Circa 2nd Century A.D.
Deep blue-green in color, the large twenty-sided die incised with a distinct symbol on each of its faces
2 1/16 in. (5.2 cm.) wide
THE PROPERTY OF A
MARYLAND FINE ARTS PROFESSOR
Acquired by the current owner's father in Egypt in the 1920s.
Several polyhedra in various materials with similar symbols are known from the Roman period. Modern scholarship has not yet established the game for which these dice were used.