Randy,
Couple of things:
1) If you are a valid Ham Radio Operator and have your license on you and you present that to a Law Enforcement Officer he will not confinscate it. He cant, not with a valid license-even if it does have police frequencies in it.(that is just one more reason that LEO's need to know the difference in radio equipment)
2)"When in doubt, turn it off."
That won't work! If a LEO notices a scanner in your vehicle whether it be on or off(depending on what state you are in) it is gone! They will take it faster than you can say your name, that is of coarse unless you have a Valid Ham License or a Permit issued by the state.
Police Scanners are not considered "Ham Equipment" therefore there is no control operator and can be confinscated unless you have a valid license to have it.
Bottom line-
Get the proper credintials! 1)Amatuer Radio License-dont just get the license to carry a scanner, enjoy the hobby and all the perks that come with it-like carrying a scanner!

2)Obtain a Permit issued by the state you live in-this is like MSP calls it...a backup to the ham license