Skull and crossbones fraternity, for short Crossword Clue

 The answer to the crossword clue "Skull and crossbones fraternity, for short" is SIGEP.

SIGEP stands for Sigma Phi Epsilon, a social fraternity founded in 1901 at Richmond College (now the University of Richmond) in Richmond, Virginia. The fraternity's badge or sign includes the three Greek letters ΣΠΕ above a skull and crossbones.

SIGEP is a member of the Interfraternity Council (IFC) and has chapters at over 250 colleges and universities in the United States and Canada. The fraternity's motto is "Friendship, Scholarship, Service."