[Brian Pfleuger]

The easiest all around solution is to just tell them, regardless of the law.

They don't care, really, they don't. They're not "Big Brother" invading your privacy, it's not a violation of any amendment to anything, it's called "common courtesy", maybe even "common sense". There is NO real downside, regardless of how many theoretical ones we can invent on the 'net, and there are PLENTY of real upsides, like putting the officer at ease, eliminating any chance of having it found, not ending up in jail, etc.