Meh. I agree that he should comply with the company's regulations on email signatures, or find a company who's regulations he finds more proper. He did (comply). Saying that his wanting to talk to an attorney about his rights is threat of use of force (ie. legal action) and therefore insubordination is a stretch. It's highly subjective. The company may very well be within their right to place him on administrative leave, regardless... But calling the guy an idiot is a leap, IMO.
IMO, saying "I'm getting an attorney" in a hyper or aggressive tone indicates that he wants to fight in court. But saying "I want to consult with an attorney about my rights" simply means, well, he wants to consult with an attorney about his rights. It doesn't necessarily imply that he intends to take any action against the company at all. It indicates that he wishes to educate himself on the issue. That should be applauded, IMO.