Well, time for some splainin'.

Fine silver is typically 99.9% pure silver. Usually used in coinage. The problem with fine silver is that it is a bit soft, so it bends, dents, dings and scratches easily making it not very suitable for jewelry. It polishes to a bright shine, but tarnishes in time as the silver oxidizes. It is typically marked .999 to indicate 99.9% pure silver.

Sterling Silver is an alloy of 92.5% silver and 7.5% of another metal, typically copper. The copper is added to give the alloy more strength making it suitable for use in jewelry. It was developed back in the 12th century. But it still tarnishes as it oxidizes over time. Sterling Silver is typically marked .925, Sterling, or some abbreviation for Sterling Silver (STER, SS, STG, STRG, etc.).

Argentium® Silver is a lesser known and more recent alloy invented in 1991. It was developed by a researcher who was trying to find a use for Germanium. He learned that using it in Sterling Silver gave some benefits to the silversmithing process, but more importantly to end users was that it resisted tarnishing over traditional Sterling Silver. Argentium® silver is typically 93.5% silver or better, so we typically see Argentium® pieces marked 935. However, it is still technically a Sterling Silver the U.S. only requires that it be marked 925 or better. 

We have seen other jewelry items marked with other numbers such as .920. In that case it would indicate that the alloy used was 92.0% silver and 8% would be some other metal(s). These may occasionally show up in our vintage jewelry, but it is not an alloy we use when making jewelry.