It would seem on the surface to be a polite sentiment from the state known for its "Minnesota Nice" attitude. In fact, it is an instructive example of "nudge" tactics by the state that eventually dictates behavior that is enforced by punitive threats.
In 1986, the state passed a secondary seat belt law, meaning that motorists could not be pulled over for not wearing the belt, but could be cited if pulled over for a separate, primary offense (e.g. speeding). The fine was modest, at $25. As of 2009 belt usage was 87%, according to an NHTSA report. For nudge-based behavioral modification, however, that relatively high rate of compliance is simply not good enough. So in June, 2009 the law was "upgraded" to primary status, so that authorities could pull over and ticket a motorist solely for not wearing the belt. Again, the fine is $25. Seems pretty reasonable for such an obviously sensible matter. Nonetheless, this evolution of the power of the state to force motorists into a behavior is an example of the imprudent use of law.
All laws ultimately are enforced at the point of a gun, or similiarly lethal weapon, even in such a small matter as a seat belt infraction. If you don't pay the $25 fine, and it accrues for too long or you try running away from it, you will eventually be arrested. Resist arrest and you may be clubbed, tasered or-- if the resistance is severe-- shot. There is no law that, at the end of some chain of events of disobediance, doesn't end in violence being inflicted on the individual by the government. This level of seriousness is why passing laws should be reserved to direct those behaviors that truly impact the rights of others: speeding, robbery, rape, murder, and so forth.
And that is why displaying a disingenuously cordial and Orwellian thank you, when in reality the individual really has no choice but to comply, should be a signal to the citizens that the government really is going too far.
One might imagine a similar sign back in the Hungary 1942: THANK YOUR FOR SQUEEZING INTO A CATTLE WAGON FOR DEPORTATION.