I have a SOG Seal Pup and have had several Spyderco's over the years. The mark at the base of the blade is the same (Seki-Japan in the same font/style) as is the scalloping patern.
SOG and Spyderco are not the same company. I sell both. Spyderco busted my stones when becoming a distributor and SOG had no problems at all. I have heard that some SOG blades are being made in China though. I can not verify this but that is the rumor. Could both companies be owned by the same parent company? That is a possibility but unlikely.