What this coin looks like (obverse, reverse, mint mark location, special features, etc.):
One very rare variety is the 1853/4 Seated Liberty Quarter which features an overdate error. This variety can be identified by noticing the 1853 date struck on top of an 1854 date. Parts of the underlying date are slightly doubled and seen about the 1853 date with parts of the "4" being seen within the "3". Parts of the "8" and "5" are sometimes doubled slightly. In addition: The right-side arrow can also be seen as slightly doubled with parts of the underlying arrow being seen just above the primary arrow.
This particular overdate error is also extremely bizarre and unusual because the 1853 date is struck over a preceding year - So the 1854 die and coin was originally produced in 1853 and was later stuck over by an 1853 die. Typically overdate errors have the newer year struck over the previous year. This is the only known quarter where the previous year is struck over a future year.
Coin valuation chart: Typical coin prices, values and worth per grade or condition - in USD