Not sure, here is a listing on ebay that shows the same type of W as yours does: http://www.ebay.com/itm/1941-Mercury-Dime-with-Doubled-Die-Obverse-DDO-002-FS-101-/221288748159 The one listed didn't sell and yours looks to be in better shape. Sorry I'm not much help.
The initials of Adolph Alexander Weinman, designer of the dime. Part of the design for that coin. Not an error. No extra value. Your coin looks to have been rather harshly cleaned, also.