If your wife is able and willing, have her announce on entering that she is bringing her husband in for assistance, and if that would make anyone uncomfortable she will wait until they are finished. That and your sign (which someone suggested and which I think it an effective way to warn people before they enter) should prevent problems with anyone except the nut jobs (who unfortunately are everywhere).
And I agree, cheers for you for making it possible for your wife to keep travelling. I am not at the point that I need help in the restroom (yet) but if I reach that point, I am blessed with a husband who would also take care of me wherever necessary.
