Matt - your van signage may produce one or two jobs, every now and again, as a direct result of people seeing it.
But that isn't the point of van signage.
A well signwritten van serves as a secondary way of reassuring potential and existing customers that they're dealing with a pro. When you roll up outside for the first time, it makes so much difference if the van is presented well.
As Derek says, it also works as a "second stage" in attracting interested neighbours.
Quite often when I ask enquirers how they first heard of my company, they say they looked us up in the directory or whatever but also say they've seen the vans around.
Roger - good point... I always drive courteously and make an effort to let people out at junctions etc because I do believe it works that way too. I have a personal dislike for a local security firm because every one of their vehicles I encounter on the road is either tailgating me, cuts me up, or I just see them generally driving like complete prats. Or is "they" just one of their drivers? Who knows, their vehicles are identical. As far as I'm concerned, if I needed a house alarm they'd be at the bottom of the list to call!