Stacking shelves, yeah some days I think I'd prefer it :

Clinton I don't fancy paying an ongoing amount for something like that. One party benefits greatly - the owner of the hoardings.
How can people stop and read it properly if they're driving past? I've never screeched to a halt by the side of the road to write down the number of a company advertising on a hoarding. You'd have to rely on people repeating your company name over and over in their head and remembering to look you up when they got home.
Imagine your advert hoarding could have reminded them they want a carpet cleaner but they may have forgotten your name since they saw the advert. They could get the directory and end up picking another firm - you could unwittingly end up creating a customer for your competitor!
With a mobile trailer I could move it around, and try to leave it where people aren't whizzing past in a car so they can digest the information a bit slower and hopefully take action.
Everyone's input is still appreciated though, I'm still trying to work out as best I can what this'll cost and if it's going to be worth it!