After a long period of good intentions, I finally printed up a "propaganda" T-shirt. The shirt is size XXL so I can wear it over whatever I happen to have on at commute-time. Perhaps when I ride past long queues of stuck-in-traffic motorists (burning that $4 gas at a ZERO MPG rate) it'll give 'em something to think about.
The shirt is already woefully outdated; it's 10 days or so old, and my mileage is now up by 150+ MPG!!