I have picked up new clients simply from the magnetic car sign I have on the back of my car.  I've performed notarizations in parking lots... one person went to local UPS store and their notary wasn't in, this person just happened to spot my sign and came running over to me.  Fellow notary Paul Williamson sells the magnetic signs in his webstore.

Another great way to advertise is on clothing.  I have 3 sweatshirts I wear to the grandkids soccer and baseball games (and around town on the weekends).  I have a huge logo on the back of them (covers the whole back) and I've received new customers from that.  I had them made at Queensboro Shirt Co.  I also have an embroidered canvas attache that hold everything really well - also from Queensboro.

I've often though about bodypainting "a car" - something like a VW to match my logo, and then put a big red feather on the antenna (or on the roof of the car like the Truly Nolan mice???)  Can't you just picture it?