Signal a u-turn to road users
First, don't attempt a u-turn at a junction where you may have vehicles approaching from multiple directions and vehicle drivers will be expecting you to make a left or right turn, not a u-turn.

U turn away at a point where you can see both directions clearly - away from blind turns and rises. Wait until vehicle have passed you to turn, If you need to get vehicles past, stop and wave them by.

You can also more safely u-turn by turning right or left onto a minor side road (or driveway, carpark etc), turning around there, then making the opposite turn back onto the major road.