They are not vintage, they are newly made. He has them all for the same price and not a single one is damaged or shows any wear, they are all in the same condition. His signs are all magazine ads cropped and photoshopped to look like a sign.
None of those Eureka signs are real at all. The one you linked to, the original image is from a comic book cover.
There is a ton of counterfeiting and scams that happen with old signs, this is one such scam.