Small "Yellow Arrows" on the roads

Does anyone know what these arrows are all about?
They are on markings at junction all over Cardiff bay and Penarth.
I thought initially is was a cycle race or a half marathon but now I have seen them at junctions in Swansea also.

I am perplexed!

here is an example of one in Penarth, the're all drawn the same style.

probably to do with water mains, or some other public service that is about to dig up the road on marine parade

They are to mark the location of underground services - yellow means gas, green is BT and other comms, red is electric, blue is water

http://www.bbc.co.uk/news/magazine-25915468

It could also be information regarding re-positioning/re-marking of Road Markings (the 'No Entry' in your pic looks like it is in need of repainting?)

Usually, with underground services markings there is some other information in addition to a simple mark.