"Number plate" is the term used for a number plate in the United Kingdom and in Europe. The plates are unique for each vehicle on the road, including motorcycles. Many catchy number plate slogans or sayings would work especially well on a motorcycle.
Cocky Plate Ideas
A single word on the back of your motorcycle conveying a thought for motorists who are stuck behind you in traffic or whom that you have just passed works well for motorcycles. A number plate that reads ZIIIP or SEEYA is effective as you cruise past motorists, especially when you squeeze between cars stuck in gridlock or slow-moving traffic. Another funny one may be AIAIAI, as if that's the sound you make as you cruise down the road. This may infuriate some of the drivers you pass, but that's the advantage to being on a motorcycle while they are stuck in less manoeuvrable cars.
Fantasy Plate Ideas
Comparing your motorcycle to a different object or animal that people ride is another good idea for your number plate, making you stand out from the rest of the traffic as an inventive motorcycle rider. A number plate that says JET or HORSE could work quite well for a fast motorcycle, or maybe HOG or MOOSE for a motorcycle meant for cruising, such as a Harley. These plates will give everyone who sees them a chuckle or at least something to think about, personally conveying what your motorcycle means to you.
Personal Plate Idea
Sometimes your number plate slogan doesn't have to be understood by everyone, just by you or a couple of friends. Your motorcycle could be named after a woman in your life or just have its own name, like SUSIE. Slogans that represent more abstract things like feelings are another good slogan idea, such FREE or JOY, which illustrate why you ride the motorcycle in the first place. That's often the case with number plate slogans: You select the sayings because they mean something to you, not everyone else.
Witty Plate Ideas
Witty, complex plates are often the best, as they make the drivers on the road behind you sit and think about your number plate and what it means. It's like a riddle on the road in front of you. A good, witty plate for a bike is XPLTV, which is "expletive" when broken down. Or for the multilingual wits out there, how about KSUPAPA, which translates from Spanish as "Who's your daddy?" The sky's the limit for witty number plates perfect for motorcycles out there -- you just have to be creative.