Matt,
This youtube explains the process:
http://www.youtube.com/watch?v=t5bgqehnjZkand I'm pretty sure the guy who put it up does this for his business.
One of the things that the guy says is that his signs are cut square to make them easier to position on the van. The company I used didn't cut them square; they didn't cut some of them at all and I had to do the cutting. And those they did cut, the backing was bigger than the the front, which meant that I still had to cut them.
I'm sure they had the cutting experience to have made this job easier for their customers.
Also, in the youtube the guy says they send the two tools you need out (a spreader (I used a tool you use for grouting tiles) and a scalpel), but this company didn't.
In the youtube the guy says they send you out the design to you (I couldn't remember what was supposed to go where), but mine didn't. So I had to fanny about looking for it on the interweb.
It also took three e-mails, two phone calls and a three week wait (granted there was loads of bank holidays) to get my goods.
However, the sign writing is of good quality (I think) and I'm pleased with the outcome, in spite of the above.
I'd definitely check out the business in the youtube though. E-mail the guy who put the link up.