Wanting to get in on this a bit... So far I can get into Sector 5 and Sector 8's bottom-right one but I'm yet to get into Sector 8 top-right. Sector 6's bottom left has something interesting.. It's the only one I've found so far that has the SI glyph, apart from the main 'stonehenge' with the dead elites. I also found some other random elites in the city somewhere with two blank glyphs. Another observation - There only seem two be two different glyphs: -thin with dots -blocky, where one glyph has a peice off to the side. All the others, as far as I can remember are locked or do not seem to have any importance. The checkpoints people seem to be getting when looking at glyphs, I believe, are just checkpoints the game does every-so-often. I also haven't been able to hear anything major when shooting the glyphs or elites in the 'stonehenge' (The sad SI symbol is already there, does not appear when you shoot the elite).