Listening to: Paradigm Shift-Rhian Sheehan
Further to a conversation with NotKate, here is some Nose Art. Good brief definition here, even if some of the photos (the more modern ones near the bottom) are actually of standard markings.
'Nose art' is a term used to describe a genre of graphic art, which is non-standard personal markings applied to aircraft (or other machinery) by their crews or owners for morale purposes, most often during wartime, but also for special occasions and exercises away from home. Themes and subjects vary widely. Such decoration is usually frowned upon by officialdom, and is normally short lived. The heyday of nose art was during the second world war, with many aircraft sporting slogans or illustrations, however the practice continues to this day (if you check out the video for the U2/Greenday song 'The saints are coming', one of the helicopters lifting people out of the water has sharks teeth painted on the nose).
This is likely the most spectacular example of all, which was worn by a bomber in the pacific near the end of world war two.
Good second world war examples here.
Slightly more modern examples here.
'Zapping' on the other hand, is kinda like graffiti, and is usually inflicted on aircraft by friendly rivals, like in the picture below where an Australian aircraft has been zapped by New Zealanders.
This is a landing gear door on an Australian fighter that I saw at an airshow in Melbourne a few years ago. The aircraft has either visited NZ, or been on exercise with New Zealanders, since someone has spraypainted the stylised markings of a New Zealand air force squadron on it, albeit in a very discreet place. It is a related sub genre of nose art, with much more spectacular examples that I know of. For example, a New Zealand air force jet that was stuck at at Australian base for a few days with mechanical problems came home with giant Australian unit markings covering most of the tail, and a British jet visiting NZ had all of its British markings replaced with NZ ones.
Markings like these and nose art in general is cool because it personalises otherwise drab and generic machines, and also shows that art can exist even in unlikely environments.