I am a licensed engineer. I worked as an engineer for my entire civilian career. That license was not an absolute requirement, but, at least in the early years (1960s, '70s, '80s) it was a always asked for.
Here's the kicker. My license was almost a joke. It was an FCC, First Class Radio-Telephone license which was supposed to be a requirement for operating and maintaining a commercial transmitter. You took a series of tests with the First Class being the last one. Why was it a joke? Because there were private schools who taught the questions on the tests. You paid them their fee and they taught you if you see such-and-such in the question, the answer is B. Never mind any understanding of what was being asked in that question, just THE ANSWER IS B. Likewise for all the other questions on all the versions that the FCC had.
How do I know? A friend of mine taught one of the classes. He had a Second Class license and took the new First Class tests when they became available. In spite of the fact that he knew every answer to every question on every version of the test, he always DELIBERATELY flunked so he could continue taking the new tests and memorize the new questions and answers. Then he would get together with the other teachers and try to figure out what answers the FCC wanted for each new question. Not, what the correct answer was, but what the FCC thought it should be. Some questions made NO SENSE. They still had to figure out what answer was considered correct. I sat in on a couple of those sessions. It was great fun.
For a fee, they guaranteed you an FCC license. It was a joke. Somewhere around the late 70s the FCC did away with the test system and issued replacement, General Class licenses to all holders. They did not expire so I guess I am still licensed by the FCC, if I can find it.
I designed and built TV stations. I operated, maintained, even modified TV transmitters. I hired and supervised others to do those things. My status has never been questioned by any state that I worked in and I have never heard of any state that did so.
As far as I know, all 50 states did not question the FCC license and do not question the title of engineer for those who work on the technical side of radio and TV stations. So I guess I am a legitimate engineer in all 50 states.