What does the stamp RSE mean on jewelry?

I have a pendant that has a square, facet cut very light yellow gem that I believe is Yellow Tourmaline, set in a silver colored metal. I believe it is Silver, but it may be White Gold. The back of it is stamped "RSE 325". The 325 stamp was explained in a separate question, but I can't for the life of me find anything out about "RSE"

The relative standard error (RSE) is a measure of the reliability of a survey statistic. The smaller the relative standard error, the more precise the estimate.