The US does not have an official language, but it does have English as the traditional default language so everything official from a government source is in English and may also be in another language.
So if there is something officially posted like traffic signs they will be in english and may also have spanish too. There are communities where all the businesses and residents post everything in another language, but someone passing through will see an english version if it is official government posted stuff like traffic signs.
Note: I haven't been literally everywhere in the nation so there might be places that don't have english on local government signage, but I would be pretty surprised.