During our summer vacation in 2003, my wife and I amused ourselves by taking leisurely drives in Ohio and photographing every diamond-shaped highway sign that we saw along the roadsides. (Well, not every sign; only the distinct ones.) For provenance, I also stood at the base of each sign and measured its GPS coordinates.
This turned out to be even more fun than a scavenger hunt, so we filled in some gaps when we returned to California. And we intend to keep adding to this collection as we drive further, although we realize that we may have to venture to New England in order to see `FROST HEAVES'.
Here are the images of our collection so far.