Silver, in it's pure form, is safe and in fact a powerful antimicrobial. I too add a little colloidal silver to Kiwi's water for a few days if I see a funny poo or he seems a little under the weather and it usually perks him right up. However, pure silver is too soft to be used in jewelry (typically). Sterling silver is not in fact pure silver and is alloyed with another metal for durability. Typically, copper, another generally bird safe metal, is used as the alloy metal but they can also use other metals, including zinc. There is no way of knowing the alloy if you didn't make the mix yourself. Lower quality silver such as "German silver" (hallmarked under .925, or less than 92.5% pure silver) shouldn't be trusted for your bird to touch. Personally though, I don't see an issue with your bird playing with a sterling ring and would be more concerned with any residues that could accumulate on it such as lotions, soaps, dead skin cells etc...
