Tibetan cry for freedom.

I agree; it looks like oṃ maṇi padme hūṃ. According to Wikipedia, the Zang looks like this:

ༀ་མ་ཎི་པད་མེ་ཧཱུྃ.

I don't read the script but it looks close enough.

How exactly did it get there, though, and how did they write it?

Very cool post.

While I have no explanation for the script you found, I think I may understand the reasons for all of the circles. I've drawn much smaller circles at the shooting range...

After retrieving my target paper I circle my bullet holes, then send the target back down range. This way I easily know what holes were already there upon the next retrieve after firing another magazine down range. This is especially vital in knowing when I missed the paper altogether...or in this case...when ordinance malfunctioned and didn't explode as it was supposed to or landed somewhere off the targeted coordinates.

They are likely circling their bomb tests for the same reason. This is why many of them have a center, just like my bullet holes are always the center of my own circles. It's an educated guess, but feasible IMO.

It could also be the target itself. They draw a thousand yard in diameter circle and aim for the center, now they can quickly identify with a satellite image how far of center the test was to it's targeted coordinate as well as quickly ascertain the crater size that was created.

The ones with multiple craters are probably cluster bomb tests.

Again cool thread. Back to reading it.