What does "sp" mean on jewelry?

The marking “SP” could mean “silver plate”; however, often silver plated items have no markings. Real silver will generally be marked “925,” “ST,” or “sterling.”

Additionally, some AVON costume jewelry is marked with the initials “SP.” The company has stated that the initials are an internal code to AVON so that they will know which vendor manufactured that particular piece. Sometimes, AVON will have multiple vendors produce the same piece of jewelry, so they want to differentiate the final products by vendor.

Saturday, September 01 2012
Source: http://www.illusionjewels.com/costumejewelrymarksa.html