Do the flags suggest any kind of pattern, ie, seen from above, would they form a grid, or are they in a straight line ? Maybe they follow a conduit underground (though not on your friend's roof I would assume) that a utility company needs to pinpoint for some reason. A bit like the orange marker posts in the UK that follow high pressure gas mains. From your previous posts I believe you live not far from the military base at Ziros, so perhaps it's something to do with them? Spooky!