Authentic Ruth Kaywoodie Sign?

[thecatspajamas]

Is there a generalized way to get a good idea whether one of these is a repro when looking at them? I'm sure that there are clues specific to each type of display/sign, and context is obviously important (as in this case), but is there some detail that is a dead giveaway on most of these? Something about the printing method that can be seen under magnification, fluorescence of the inks or card stock under black light, something like that?

It does seem from reading all the posts that the repros far outnumber the real signs, but unless they are fantasy pieces, the real signs do exist. I've yet to deal with one of these personally, original or repro, but I'm sure I will sooner or later and am wondering if there is a quick way to spot most repros? It would make me a lot less hesitant to handle them if I knew what to look for.