What does the road sign with a blue background, red circle and red x mean?

A round road sign with a blue background, red outline, and a red X through it is a sign that means no stopping.

A round sign outlined in red with a single red line diagonally across it means no waiting.

Any sign with a red circle around it tends to be prohibitive; no right turn, no left turn, no U-turns.

Signs with a blue circle around them are usually positive and indicate one-way traffic or that you should turn left turn ahead.

A London-based graphic designer recently won the £1000 first prize in the InTandem competition sponsored by the UK's first driving feedback service, How’s My Driving, by designing a new sign for display on the back of HGVs that reminds cyclists that it is dangerous to ride on their left side.