There are more than 1 manu who makes these signs. I'd say the seller is likely purchasing from one of these and then simply flipping them, or aging them more first?
http://www.ebay.com/sch/Reproduction...7228198/i.html
http://mancavecollection.com/retro-s...ll%20Signs.htm
http://www.retroplanet.com/CTGY/MLB-Baseball-Signs.html