Sue, I'd love to see these when you're done...we've kicked around the same idea in this college town.
I wish I had some cute ideas to offer...but I'm pretty frumpy. I agree that anything that reinforces the wrong idea that bikes belong in the gutter is just a little too "out there"; with a picture from a steering wheel, I'd say "get it right...stay left...and be in my sight"
For being predictable...something like "this when being straight is cool..."
A pair of converse covered shoes on the pedals of a bike in motion with the caption "goody two shoes"
If you don't grow where you're planted, you'll never BLOOM - Will Rogers