What signs exist and what signs do not exist
Note that in the definitions, he specifies that words painted on vehicles do not exist. So if a company has used a huge semi truck as a billboard, that sign does not exist because it is on a vehicle.
Some businesses use signs in or on vehicles to get around city ordnances the same way.
So if you have a lettered instruction that says pause two minutes at "rally" and you pass Rally Trucking but their sign is on a truck, don't pause.