From what I recall, there isn't a single, always-effective way to safely get a tailgator to back off or pass.
I just checked, and the MN Drivers Manual has this to say: "If the vehicle behind you is following too closely, slow down slightly and allow it to pass." This matches what I recall from Driver's Ed, too. Doesn't mean that the person doing the following isn't going to get angry and ride closer, of course, or pass you, nearly cut you off, and brake-check you in retaliation.
Road rage is always a potential problem, of course. If it seems safer to speed up and get out of their way - like taking a turnoff or similar - maybe that's the best course of action.
The trouble with bumper stickers is that it could potentially be used against you if there's an accident. Same with talking about "seeing a squirrel/dog/moose/deer/etc."
Different states have different cultures about it, too - I've heard that in places like rural parts of Texas it's common for the slower driver to pull over/off the traffic lane and let the faster drivers pass.
Basically, drive safely and mostly ignore tailgators. In my experience they usually turn off at the next big interchange, get bored and pass you, or back off within a mile or so. You'll want to keep aware of them, of course, but try not to get your back all tensed up about it - not worth the pain. (I'm working on this myself - not easy. But I'm driving legally and safely and generally within 2mph of the limit, so it isn't up to me to make them happy.)
We had a thread about this in the past:
How do you handle EXTREME tailgaters?
Found this one too:
Michigan Tailgators (Aggressive Driving Report Form)
I've got all sorts of creative, generally illegal (or borderline, at least not safe) ideas. I try not to indulge those fantasies too much, as it's no better for me than worrying about what the tailgator thinks of me.