The answer to your question is research. First you must determine
which country the item is from.
If the item is from the U.S. you may want to check the book American
Jewelry Manufacturers by Dorothy Rainwater and published by
Schiffer. Jewelers Circular Keystone also publishes updated editions
of the Brand Name & Trademark Guide.
If the item is from another country you must first determine which
country. The most is available on England, Scotland and
Ireland. Try Jackson’s Silver & Gold Marks edited by Ian Pickford.
Another good resource is The book of old Silver by Seymour B. Wyler.
There are also some websites that have Hallmark Just do
a search of the term Hallmarks to see what comes up.
I have spent many years working with and researching Antique Jewelry
and I will tell you that sometimes it is a challenge determining who
made a piece. Determining which country a piece is from is often a
challenge as well but there are clues that can be learned over time.
Custom Jewelry - Handmade Jewelry - Antique Jewelry