What This Coin Looks Like (Obverse, Reverse, Mint Mark Location, Special Features, etc.): The San Francisco Mint produced two different varieties of the 1981 S Proof Lincoln Memorial Cent (Penny) where one had a filled in S and the other had a Clear S. Depicted in the example image of the coin above is the Type 2 Clear S. This can be best identified by the S being clearer and not as filled in. It is also "flatter" in a vertical sense. Below is a close-up image comparing the Type 1 Filled S vs the Type 2 Clear S. Click the image to enlarge:
Coin Value Chart: Typical Coin Prices, Values and Worth in USD based on Grade/Condition