From the search. it seems GM initially trademarked it in 2001 so GM had exclusive rights to put the logo on mugs, t-shirts, key fobs, umbrellas, and whatever else the name might get slapped on.
I'm guessing they simply TM'd the name again, this time specifically to automobiles so that no other companies can take it for their liking. Possibly some laws were changed that requires GM to reg the name specifically for autos. Or maybe someone in their legal dept simply overlooked it years ago. Regardless, I don't think this is very much indicative of their intent to reuse it for the SS, if that's what the intent was of the original post.