Only real way of know is to buy some silver testing solution. Put a drop on the corner. If it turns green or yellow than it is probably aluminum. If it turns dark brown or reddish then it is silver. It will also brighten aluminum and have little or no effect on silver.
Or put a drop of muriatic acid (common pool acid) on it... if its silver there will be no reaction but on that it will sizzle and smoke.
It's just your ordinary garden variety aluminum name tag from a dog collar