Yea abit of a hard one, heys.....
like Half the time YOU either see a sign stated No U-turn allowed.. and then other times there nothing there at all...

.. I think if theres nothing there u should be allowed to do a U-turn,, But with care. ( give way to other cars ) e.g other flow has right of way.
and then u do see a U-turn is allowed/ or u see a U-turn arrow on the road. and U turn lights ..

They dont make it real easy..
But yea, if not sure best to prolly not do the u-turn in the 1st place. hey