making a loose fist with the thumb between the index and middle fingers, top of the thumb sticking out

This is a "t"in finger spelling used by the deaf.
http://dww.deafworldweb.org/asl/abc/az.html
The gestures are pictured.
In ASL if you waggle the fist while making the gesture it means "toilet." Along with a questioning look it may mean "Where is the Ladies' or Men's room?"
wow