The Spahn card in the '59 Venezuelan set always has the Venezuelan trademark. While some of the cards do have the US trademark, they are consistent throughout, for instance, every Venezuelan copy of Spahn will have the Venezuelan trademark line, while every Ford Frick will have the US trademark. Additionally on Spahn, to address another issue posed, the Venezuelan versions do not have any variations with his year of birth. It is always 21.
Even if you were not aware of the trademark issues, the cards are still easily identifiable just by sight. The majority of 1st series Venezuelan cards (1-110) you might come across will be found with gray backs. You will never find a US Topps card 1-110 with a gray back. Rarely, you can find a '59 Venezuelan card with a cream colored back, but it looks nothing remotely close to the bright cream color of the US issue. It's a much more dull appearance and darker cream color. All cards in the Venezuelan set were issued on both gray and cream colored stock.
There are multiple pictures of these cards available for identification purposes at the Yahoo Group:
Topps Venezuela