It's actually a common repro, and if I may be granted leave to contradict, an extremely poor one! The "weathering" makes them look a bit more genuine, but the font used and the size are utterly unlike that used by the GSWR. This is the case with almost all repros - I have never seen a convincing one of any type of sign.
Thats good, though. It would be a very bad thing if ebay eras were able to pass duds off as genuine.
I agree with comments above about these things dvaljing the price of genuine artefacts, but the other side of the coin is that they're "fun" ornaments for many - you see them in pubs etc....
Seems to me that the most common reproductions are GSWR gate (square) signs about being fined forty shillings, with various real and fictitious railway company initials at the top, long "LNER" gate signs, and larger GSWR trespass ones. None, thankfully, are likely to be confused with the real thing.
Occasionally I see them on eBay offered as genuine. I tend to contact the seller in case they don't know, and give them the benefit of the doubt, but if they don't change their ad to "repro" I have reported several sellers. I would encourage others to do the same.