Amber lens are used for turn signals. European countries have this as a requirement. I don't think the USA has a law that states as such, but most car manufacturers have used amber lens for turn signals since the 1970's. Breezie
Not sure what state you are in, but in the 1950's many commercial license tags had renewal tabs like that that screwed onto the tags. Might do a google search for 1956 commercial license tags in your state.