I heard a story that a certain Maritime Sqn painted their Sqn Number on their hangar roof in roman numerals. One night, personnel from a similar type Sqn crept onto the roof and added a couple of extra letters. The result was the word "CXXTS" on the said hangar.
(off thread, but a similar thing was tried with a French Mirage during GW2. The White UN on the tail was to have been modified by the addition of the letters C..TS, but the raiding party was discovered by security before it could take place).