As would a human given a sufficiently official-looking stop sign. In fact I think it's actually impossible for an automated car or human without figuring out the "troublemaker"'s identity whether the stop sign is fake or not. And it's not always possible to pin down someone's identity (if the person is wearing a brightly colored construction vest what do you do?).
There's a lot of construction in our neighborhood right now which made me start thinking about that possibility. It kind of sounds like something out of a heist movie (or taken to the extreme, Die Hard With a Vengance?), but really, who would know and care enough to ask the questions to notice something like that?