Outdoor advertising is the most selfish of all advertising media. It forces you to look at it by blocking the 'would be' beautiful scenery, and gives you, the viewer, nothing in return.
I have found the first example (that I have seen), of an Outdoor ad that offers a fair exchange. That is, it gives you something in return for looking at it.
You simply point your phone at it and send a picture message to your friends or loved ones.
Useful. Fun. Fair.
There is a close runner up as the most useful exchange in an outdoor ad. A few years back now, iPod installed a headphone jack so that passers by can plug in their iPod headphones and listen to a new release song that is, you guessed it, available for download on iTunes. It iStinks but in fairness does offer something for the exchange, kind of.