A couple of things that might help, though neither is a guarantee on its own.
1. The more common stainless steels are either non magnetic, or only very slightly magnetic. Silver steel is magnetic. Check if attracted to a magnet. Magnetic stainless steels do exist though.
2. Silver steel is typically supplied ground very precisely to nominal size, and commonly in 13" lengths – a close look at surface finish and checking size may be enough to separate the two materials.