The flag of Gibraltar is one of most curious cases of symbolic transfer. It's currently carried as a strong symbol of loyalty to the British crown (as you can see on these photos), what strongly contradicts its historical origins.
This is the flag of Gibraltar:
This flag is a banner of arms (a rectangular version of a coat of arms) of Gibraltar. Although confirmed by the College of Arms after the English conquest of the rock, the original grant of arms was made by Queen Isabella the Catholic, of Castile, commemorating the Spanish "re-conquest" of the place.
And the coat of arms and, consequently, the flag, is emerged in Spanish symbolism: the castle is pun on "Castile" and the biggest symbol of that kingdom, now part of Spain. The key represents the nickname of "key of Spain", although this metaphor has its origins at the time the Arabs still controlled the rock.
The most ironic thing on this flag becoming a symbol of loyalty to the British crown, in my opinion, is the fact that the Spanish never stopped using it as their own symbol. At the English takeover of the rock, most of Spanish residents of Gibraltar moved to a recently-established city called San Roque (notice the pun on "St. Rock"). As most of San Roque's earlier government was strongly linked to Spanish Gibraltarian one, they kept using the coat of arms, and now fly this flag:
A "Gibraltarian" flag with a Spanish crown. Yes, this is something that would cause much confusion to an unsuspecting.
Comments are welcome.