This sounds horrifying !
Even large yachts ( I'm thinking of 160' masts & a bit less) have a flashing red light on top - even if regulations don't force one to, anyone with a brain or conscience would make it bloody obvious, day or night, and ensure that such things are known to NOTAMS or similar as they plan it.
The point about telephone masts trying to be clandestine is a good one - recently in Horsham West Sussex ( not a low flying area except for the odd police helo ) a lot of people wondered why their car immobilisers wouldn't let them get going; turns out a 'phone mast had been secretly erected nearby, obviously trying to avoid protestors - it's well camouflaged for a change, but obviously a problem from various viewponts.
Are these bastards allowed to just chuck up these things without notifying aircraft / planning permission ?!