To be completely 'safe' I would suggest placing it, unloaded, in a case in the trunk.
In all honesty, like everything else, it depends on the officer/deputy/trooper who you may come in contact with. Personally, if I can plainly see the person is a law-abiding citizen, with no known history, or no 'alerts' when I run his name/dob, and most importantly, I don't get that little 'tingle' telling me something is wrong, I could care less if he is carrying openly, concealed, on his front seat, ect.
On the flip side, I know guys whom, if you told them you had a locked, unloaded handgun in the trunk, would want to pull you out of the car, search it, detain you, search your various body cavities, then write you tickets until their hands cramped.
As I tell my subordinates, you can never go wrong using your gut, and some common sense.
