It varies from state to state, but the general rule is, it is not legal to have your license plate mounted vertically. Most states have a law that requires your license plate to be mounted horizontally so it can be read from left to right, just like a book. That being said, it is rare for a police officer to actually enforce this law, but you really don’t want to give them a reason to pull you over. Many custom license plate mounting brackets
allow the plate to be bolted in either a horizontal or vertical position, which gives you multiple options without having to change your license plate bracket.