Intaglio Mint Round .999 Silver Question

I bought a 2oz Mercury Dime silver round from the Intaglio Mint for a B-Day present. This is my first purchase from them. I received it today and it's beautiful. On the round it states two ounces, but I don't see anything indicating it's. 999 silver or any other purity. Is it just universally known their rounds are .999 silver? If we ever want to sell it, will anyone question it's .999 silver? What gives?