What this coin looks like (obverse, reverse, mint mark location, special features, etc.): This 1918 D Indian Head / Buffalo Nickel is a very rare and valuable date overstamp error. The Denver Mint stamped the 1918 date over the 1917 date. It is very easy to spot this coin as the 8 is stamped over a very noticeable 7. Depicted in the image above are arrows pointing out the 7 - which includes a flat-topped 8 and straight lines within the 8 itself.
Coin valuation chart: Typical coin prices, values and worth per grade or condition - in USD