When you examine the rules its amazing what is actually permitted. Firstly there is visual range. Notionally as long as you can see it (notionally 400m horizontally and 400 ft vertically) then they can fly them without telling anyone. Secondly there is mass. As long as its below 7kg they can fly it without telling anyone. Thirdly there is cameras...as long as it doesn't carry one its a Small Unmanned Aircraft (SUA). And the best bit? They can fly them inside an ATZ without asking any permission. We found someone in ours and checked the rules.
However if they carry a camera they become a Small Unmanned Surveillance Aircraft (SUSA) which can trip them up for capturing pictures of people who haven't given permission. I think its some data protection law that applies.
Of course if they flew around in your departure lane that's reckless endangerment but its probably too late because you'll have hit them.
So in summary, below 400ft a 7kg UAV is perfectly legal and could be found anywhere. Above that they are arguably outside visual range and you could arguably report them. Good luck