That is a good idea. At least with door hangers, you don't have to worry about how to get them to the homeowners. I also include the bit about a free tune-up with all repairs. It is just something I always do to make the computer run right.
I have noticed that there are wide varying views about what makes a PC tune-up. Mine usually take 3-4 hours to complete but it also includes 2 virus scans, adware removal, delete useless files, set security settings, disk drive logical & surface scans, install free utilities, driver updates, OS patches, dust cleaning, etc. It is really a lot of work.
I worked on a PC about four weeks ago, and the owner said she had paid someone $40 for maintenance on the PC at the first of the year. I had to tell the lady that someone ripped her off. The fan blades and heatsinks were clogged with dust, there were over 100 updates for the SW not loaded, the event viewer was full of errors, the system took 4 minutes to boot, etc. etc. I took the computer and performed my regular tune-up. When I brought it back, the owner said the PC ran faster than it did when it was new. I wasn't surprised but I sure cannot do that for $40 either.
One of the best advertisements to keep your name in front of them is to give away mouse pads but they are rather expensive. Another good one is to sponsor a local kids sports team (soccer, softball, etc.) with T-shirts with your company name on them. Lots of parents will see those shirts.