How to identify Silver authenticity ?
Firstly look for a Hallmarking , generally starts with a TRIANGLE symbol followed by purity.
Secondly look for Stamp of the item some of the general stamps in all purity we are listing below for your references
999 , T-97 , RSG100 , 925 , ST. SILVER , T-100 , 925 SILVER. , T70. T65 , S.T.S.C. , SJP , KPT , श्री RSG , श्रीJI , श्री KAILASH
Thirdly if the items is not turning black even if exposed to moisture and air than go to any nearby jeweller and get it tested.