Glenn said:

        To identify ourselves to (a) oncoming cars as well as (b) cars
        overtaking us, we could use two stickers -- one for the front,
        one for the rear.....

Call me Mr. Conservative, but I would much prefer that drivers who are
headed my way at a terrifying rate of speed pay attention to missing me and
the rest of the folks on the road, not looking for my sticker (or the lack
thereof). And as much of my driving includes many miles on multi-lane and
divided hwys, I doubt that a sticker on the front of the van would be
visible unless it was one x two feet or larger.

I visualize modest sized stickers on the back and side windows (at the
rear).  Most everybody passes me, especially in the mountains and this
would give them the opportunity to check out the sticker and perhaps wave.
(Since I regularly get flipped off, a wave indicating solidarity would be
nice.)

My thoughts on the subject,

David