U.S. and Worldwide Stamps and Postal History

1915 Gatun Locks, 5c blue and black, center inverted, well centered, tied by violet "Agencia Postal Feb 23 1916 Panama" cancel on cover addressed locally in Panama City, additional postmark (arrival?) repeated on back, central filing fold well away from the stamp, fine-v.f., with 2009 Philatelic Foundation certificate. One of only a few known 5c inverted centers used on cover, ex-Cunliffe
Estimate: $2500