I've been thinking about this on and off since you posted the question, and the one feature that I can think of I describe below. But it's phonemically contrastive only in certain phonemic contexts.
BSL has a handshape usually called F
(this is formed by making a circle with the index finger and thumb). This handshape is usually called 9
in literature about ASL. In ASL a feature which could be called something like "roundedness" (not the same as roundedness in spoken languages!) It's about how round that circle is. So ASL actually has two handshapes, 9
and Flat9
. These two are phonemically contrastive, like how English contrasts h and b because hinge is different from binge.