This is for consistency with strings; Signals operate like strings (i.e. sig[0] is another Signal like with strings rather than element type like most collections, they can be sliced, etc.), so for consistency __contains__ should support finding longer substrings than the one-bit case. (The windowing comparisons are also a little annoying to write out by hand, so it would be handy to have around, even if it's not necessarily a terribly common operation.)