Why don't you look at (for example) Arizona's legal requirements for getting a driver's license. I'll admit it took me a whole 30 seconds to get them on Google. Having a legal license from the State of Arizona does actually prove that you are either a citizen or legally in the country, because that is the only way that Arizona will issue a license to you. Idaho is the same way; no birth certificate, no green card, no legal papers = no license. So, is it completely foolproof, no. You could get your license with faked documents, or just a fake license, which just adds to your crimes, but a legal, valid license certainly does imply your legal status.