There's a live auction house listing coins on
ebay, but they do not indicate mint marks in the title or description. One auction is for an 1899 Morgan, but the coin in the listing is an 1899-O Morgan which is worth much less. Pics are not great. I contacted them, but all they did was state that their terms and conditions free them from the responsibility of listing errors and thanked me for contacting them. Here's one of the listings:
http://cgi.ebay.com/301759805235