I have seen people doing this with affiliate redirects.
If you only distribute a sticker with your logo and slogan, how will they know where to go? Or are you trying to create awareness for your slogan and logo? Why not create magnetic prints and just put them on their cars? It is not that expensive to print on magnetic paper. You could do it yourself for example. But if you want to go with the stickers, just do it.
Yes, it is really good idea to increase leads and promote your business. You can use Email marketing to increase leads. This is another good method of marketing of products and services choose target mailing list to get success.
I actually got a dollar bill the other day that had a small round sticker on the back covering the eagle that said something like turn this $1 into $100 learn how at: It really got my attention as I never seen this done before with a sticker, so I would do something like this if I were you as one way to market. Also I have seen people using a rubber stamp with their website url and stamping money along the white border, but I think it might be against the law to stamp money, so I would stick with sticker, no punt intended