This flag pictorial cancellation indirectly fits the topic, so I thought I'd post it:

In the event you can't make out the flags in the rubber stamp cancel, it's the USA, US Confederacy, UK, France and Spain (in that order) ... all of which flew in Pensacola, Florida at one time or another in it's history, as illustrated on their web site:
http://www.fiestaoffiveflags.org/By the way, the US Forever Flag Stamp cancelled on this cover is from the ATM Booklet of Lady Liberty/Flag Stamps, which is a less common variety, easily set apart not only because of the straight edge, but because of the "granier" blue background.