In the Collector's Guide by Caroline & Nick Pope you will find a list of the known painters with number-signature and their working period at Royal Copenhagen.
Also the data of the designing artist will be an important indication of possible age.
While American manufacturers did not apply assay marks, city marks or date marks, they did apply a maker's mark. The old hallmarks were as unique as today's logos, and disputes often arose when one company copied another's stamp.
The name of the artist or manufacturer may now be used for this." Between 18, Austria-Hungary and later, Hungary used the crescent moon crowned head of antique Greek heroine Diana as the hallmarking symbol of legal silver alloys.
The head was encircled by a frame, optionally composed of convex, concave and straight lines.
Meanwhile, a hexagonal frame represented 900 fine silver.
The same logic was also used to frame gold hallmarks.