Bigger than normal ring. Looks good when mixed with other. Looks best on pinky finger. More often in gold. The post is dadicated to a signet ring. These are getting more popular now. You should definitely know where you can buy them.
Above, few of my own pictures to get you inspired - below, a selection of best designs I found. The Gold&Terra (I personally own and it's pictured above) and Sarah&Sebastian (on my wishlist) are my favourites.