Don't ever underestimate the power of a smiley face. The council of South Lanarckshire in Scotland added a simple face to road signs that tell drivers their speed: smiley face if they're under the speed limit and sad face if they're over.
That simple addition resulted in the numbers of speeders being reduced by 53%: Link - via Barking up the wrong tree
The idea is basically that each and every element of our experience contrasts each other element of our experience. Such that; the addition or subtraction of a smiley face in the periphery of our visual field can make or break a decision. The way I've attempted to express this is someway of having a perceived object projected through a lens which contains contextual information. In this case when I look down at my speedometer, I don't just see a plain speedometer, I see it through the lens of the smiley/sad face and what it signifies, and whatever else I have been experiencing. If I get into an argument early in the day and get behind the wheel, that argument is going to color my driving experience and probably encourage a heavier foot.
This may seem obvious, that our experiences affect each other at least this much, but I'm looking for an illustration or thought experiment that can make the extent of these influences more obvious.
So, it's illegal to text while you drive, but legal for the sign to text you while you drive.