The mint mark, if any, is found on the reverse - next to the E in ONE. If you can post a pic of the reverse as well we can give you an idea of the value of the coin.
This is a mercery Dime and I don't believe it to be of high value in any mintmark. http://cgi.ebay.com/1945-P-D-AND-S-...363832406QQcategoryZ41092QQrdZ1QQcmdZViewItem
As already noted it is a 1945S Mercury Dime and very common. At coin shows around here, that one would sell for about $1. However, if you tried to sell it there, you would be lucky to get anything over silver value. Keep on looking.