As a beginning metalsmith, you may want to consider using a “.925” or “sterling” hallmark stamp, so your customers know what type of silver you used in your work. Fine silver can be marked with a ".999" stamp.
“Sterling” and other metal-identification stamps are available from jewelry-tool suppliers. Rio Grande carries all three. Signature hallmarks must be registered, are primarily for trade manufacturers (they cost $50–$250), and can be ordered from specialty stamp makers.
To stamp the metal with a hallmark, place the metal on a hard metal surface, such as an anvil, and align the stamp in the center. Hold the stamp firmly in place, and use a heavy hammer to strike the stamp once. The stamp should make a clear, single impression with an even depth all over. If you’re using a signature hallmark, repeat the procedure with that stamp.