This mint error is easily determined by the bowl shaped U on UNITED on the 2007 reverse as opposed to the new "U" font on the 2008 reverse.
There are numerous changes on the reverse of the 2008 W American Silver Eagle including flatter, larger, and closer stars above the eagle. Special Burnished Coin Graded MS-70 by PCGS!
Note: PCGS has, at different times, denoted the special burnished finish on these coins with either the "MS" or "SP" designation. These are identical in both meaning and value. Coins sold through this listing may bear either designation.