Antler polyomino
An antler is a polyomino that is diagonally directed, called such since they look like one of a deer's antlers.
A polyomino that is directed in a diagonal is orthogonally directed in each of the directions that make up that diagonal. Thus, an antler is a bent tree. Specifically, it is a bent tree that has only one anchor cell.
Symbol
Regex
ru(ru|lu|ld(ld)*lu)*ld(ld)*