If it brightens up the day for someone, to wear pink fluffy ears on thier helmet, and allows them to express how happy they are, or prevents them from being sour/bitter/depressed/sad then i approve wholeheartedly.
Same goes for self help messages on top tubes, My Little Pony bells bought by daughters, and anything else that brings some light into what might otherwise be a dark and shitty life.
One of the best things i have bought are cycling gloves that have smileys on the back and palm. They remind me to smile and i have definitely had positive reactions from car drivers, when signalling my turns.