License plates first started to be on cars in 1901, and most states were in compliance with new law, by 1930. The law was enacted to keep track of cars and their owner who were involved in car accidents. Idaho was the first state to add graphics to the metal plates, in 1928. They had a picture of a potato. Today plates would be referred to as a Vintage Idaho License Plates.
Some vintage plates have products on them, but they are a must have item, for many vintage collector enthusiasts. A lot of people collect them purely as a hobby, others have cultivated thriving businesses, as part of a larger vintage artifact collection. So maybe a spring cleaning will turn up some Vintage Idaho License Plates.