Three signs similar to this one have been stolen

Eleven of the hi-tech units worth �10,000 each were put up by the county council as part of a road safety drive.

But thieves armed either with a ladder or crane have taken three even though they stand five metres above ground.

Two of the signs have disappeared from near the school in Peniel and the other from Dyffryn Road in Ammanford.

The council's head of transport Trevor Sage said the signs were recently introduced at strategic locations as part of a road safety campaign.

Motorists travelling too fast past an infra-red sensor are warned by the signs to slow down.

They are not booked or fined but simply reminded of the speed limit in both English and Welsh.

"It could be someone with a grievance who thinks, completely wrongly, that they are being booked for speeding," said Mr Sage.

But he said the more likely explanation was it was "someone who is taking them to generate electricity".

Police believe at least two people are responsible as the panels were bolted to the top of the poles.

This sign is one of the ones that was stolen

A spokesman for Dyfed-Powys Police said: "It would have taken at least two men some time to get the panels down.

"The perpetrators would have had to have used a cherry picker or a high lifting machine to get them down."

Mr Sage said the signs had been particularly effective in reducing speeds near Peniel School from where two were taken.

"These panels are there for road safety purposes and have proved very effective, we have had a lot of positive feedback from communities," he added.

"Stealing them is risking lives and really compromising road safety."

Police have appealed for anyone with information to contact their local police station.