Random thought I had. How about a checksum type scheme which is reflected by a visual cue, like the color of the nym (or it could be anything else, whatever is least intrusive)

That way you can quickly see at a moments glance that the user is not the same as the one you're used to seeing

I guess it wouldn't help new users who don't know the "color" of the genuine vs the "color" of the fake, but that should be pretty quick to pick up

I'm trying to avoid resorting to any kind of centralized or even community driven censorship.