Sign language
If you have ever heard a motorcycle zoom by, then you would probably know they can be very loud at times. Deafening even, to the point where you can barely hear your own thoughts as they drive by. So just how do they talk to each other as they ride these beasts?
Well, they have developed a certain type of sign language that they all use as they ride. Because of the loud noise, it was necessary to develop this in order to communicate properly out on the road. A raised single finger or a tap on the helmet can all mean their own specific thing.