I will never understand the impulse to plaster your car with your life philosophy. Obviously this is another level, but even the stick figure families or whatever are kind of weird. Some of it is sensitive information that you're just shouting out into the world.

For example, there's this person I see around my town whose license plate is "2HOUSES". So you're advertising to potential thieves that you're rich enough to afford 2 houses and that you're definitely not currently at either of them. Incredibly stupid just for the vanity of it, but you're also and just making a target of yourself.