The 1854-O Huge O Quarter Dollar is a very unusual variety, because the mintmark is large, misshapen, and unlike the O mintmark on any other coin from this year or from any other. For this reason, experts believe the mintmark was either re-worked or added by hand to a die that the Philadelphia Mint shipped to New Orleans minus a mintmark (the Philadelphia Mint supplied all the dies to the branch mints, and added the mintmarks before shipping out the dies). A similar situation occured in 1870, when the San Francisco Mint received a reverse die for a Three-Dollar Gold piece without a mintmark, leading to the unique 1870-S $3 gold piece. Walter Breen claimed to have discovered the 1854-O Huge O Quarter Dollar in 1954, exactly one hundred years after its issuance.
According to the PCGS Population Report, the certified population of the 1854-O Huge O is roughly half that of the regular 1854-O Quarter Dollar, making it scarce but not rare. Larry Briggs noted the existence of a single Uncirculated example, but gave no other information. No Mint State examples have been certified by PCGS. Rather, the finest examples graded by them are two AU-58's. Since 1994, the highest price realized at auction by an 1854-O Huge O Quarter Dollar was $12,075 (PCGS estimated grade XF45) in a July 2005 auction.
Sources and/or recommended reading:
Briggs, Larry. The Comprehensive Encyclopedia of United States Liberty Seated Quarters. Lima, OH, Larry Briggs, 1991.