@engineer,
I don't know how it works now anywhere, but when I was in, people in civilian clothes weren't generally saluted. In fact I recall some idiot Captain (supposedly) in civvies getting in my face once (why isn't worth getting into) going "I'm a Captain!" I said "Really? Can I see some ID?" She declined so I ignored her...
In fact I'll go one better: I was once walking into the BX and a full bird was coming out. I was about to salute, but he purposely looked the other direction, so I didn't. His son was with him and you should have his mouth drop open, lol. Hey I'm not going to salute the air. Needless to say the Colonel just kept walking.
Thanks for the replies!