Since I don't know what they are, I let my anxiety go all wacko over their potential purposes. No, really...it's fun! For instance, they could be detection devices, that record passersby identity by reading the microchip that we were all implanted with when we thought we were getting a vaccine (thank you X-Files!). Or maybe they are detection devices but they're looking for people listening to bad music...that's why your favorite song goes fuzzy on the radio...they're trying to protect you from yourself. Or perhaps it's not a detector, but a beacon, letting the circling alien mother ships know they have successfully assimilated themselves into our world and are awaiting further instructions. But it could be nothing at all like that. In fact, this could very well be just like a geocache, but instead of using multi-million-dollar satellites to find tupperware hidden in the woods, you get points for placing these in the most random locations.
And if you don't know what it is, take a guess!