I love my city but I can see how this would be true for non-Bostonians. If Boston is your home you do just know, in the sense that you know other drivers may not know or care so you are on the lookout for them. You just curse those drivers when you think the've done the wrong thing and move on.

Still have to say though that this is less of an issue recently. Many fewer missing traffic signs than there used to be. I don't care for it :)