I think it's the style or pattern number? Many silver company's put numbers like that on their products. Yes I agree it's the top of a brush and was part of a vanity set, which would maybe have a hand mirror, finger nail buffer and other items with all the same pattern on them. I believe the same number would maybe be on all the pieces of the set, so if you lost one it be easier to run down a replacement with the maker and that number.??
Did you weigh that piece? It's definitely worth it weight in silver.