I like signage, premiums and promotional items from the prewar period and pick them up where I can. Owing to what I collect I also am frequently confronted with uncataloged items and have to make a judgment call on acquisition. I tend to analyze such items as follows:
Does it match with what I know about similar materials from the era? I have never seen a single color sign on crappy chipboard with a major celebrity promotion for a major consumer company. Generally, when it comes to prewar signage from consumer companies advertising with a celebrity, you just do not see them made like that. The companies put a lot more effort into their pieces than that and the stuff usually looks a lot nicer than what has been shown here. The only exception I run across regularly are handbill-type pieces from movies, but they are flyers, not signs, and are printed on paper. Here is an example:
That's strike 1.
What is the company involved? Coca Cola is one of the best-cataloged, most widely collected brands ever. Their classic baseball-related signage is well known and well documented. For an uncataloged Coke piece featuring the most valuable subject [baseball] and a HOFer to boot to pop up after nearly 100 years strains credulity.
That's strike 2.
Last, there is the source and the price. A real 1910-1920 Coca Cola piece featuring a baseball HOFer would be worth a fortune and would not surface from some no-name seller offering it for $50.
Strike 3.
Am I right every time? Of course not. I am sure I've missed some gems over the years [off the top of my head I can recall and regret passing on a 1929 A's premium a few years ago at a National, and a Joe Louis piece as well], but I haven't been burned in a long time either.