My uncle owned an airport in Paramus, NJ in the '30s and pointed out several of these to me as a child - it seems these were the 'original' waymarks for aviators, marking the names of towns (and some advertising) just to be visible from the air. That's where the idea comes from.
I wasn't aware that there are sites that offer this type of thing -- another sign that I am spending way-too-much time on this one...?