Would this be a unique investment? A sterling silver mercury dime ring? Source: http://flintski.com/SmoothMercuryDime_Z.jpg
I have seen a few coin rings, pendants and watches. Destroys any numismatic value in the coin but most of the coins are given a nice polish to get them shiny first so not much value in them anyway. One of the guys in the coin club brought in a clock with a 1946 Penny as the clock face, the coin alone was worth more than the whole item, before it was drilled. Gold sovereign rings are quite popular.