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The maker's mark WERNERiSa is from Warsaw under Russian rule. Poland as a country didn't exist 1795-1918. The maker (founder/owner) is August Teodor Werner 1864-1902. The anchor is his trade mark/logo, typical for companies in Warsaw at that time. The assayer OC is Osip/Jozéf/Ios Sosnkowsky who assayed in Warsaw 1862-1896.
You're welcome. Information can be found in books, sites like this, visiting museums, antique shops, auctions and fairs etc.... This is the way to gain experience but it takes years....and of course internet, but you have to be a bit careful with internet because anybody can write whatever in it.