I have 72 set as my line wrap, and that also wraps my sigs.
The reasoning for 72 is to allow a couple of quote depths without hard wrapping at 80 (for all those people reading on a teletype!), but sigs are not quoted so don't need the same handling.
I'd suggest sigs being presented as-is, rather than wrapped by the editor before posting.
Or a tickbox, like the "Enable wrapping quoted text at 80 characters"