The simple act of pinging one of these coins will give off a unique sound wave you can either tell by ear, or you can hold it up to the microphone of a cellphone and your free cellphone app will tell you if the resonance matches and if it's real or not. A fake silver alloy will not pass.
Last time I saw you post that, I responded asking for a link to -- or at least the name of -- that app. Unless I missed it, you did not reply.
There's not just one, there's tons of them. This is not science rocket people, it's just measuring a sound wave.