First off, I think you are welcome here on orr.net!
But to answer your question, I don't think the FCC much cares anymore. If I'm doing operations outside of the 4th call zone I will ID by saying "KU4OJ portable 5" just to make the oldtimers happy.
Sometimes when traveling away from home I will sign KU4OJ/mobile just to let the locals know I'm on the road and not familiar with the area or its repeaters. But that's just what I do.
Again, welcome to the forum!