We found this at Seal Sands on Teeside. A lot of pipe lines run through the area. It turns out that it is a sacrificial metal anode that is more reactive than the metal in the pipeline. It is set up to make the pipeline the cathode (negative terminal) of an electrochemical cell. Metals make positive ions so they would tend to join the negative cathode. That means ions would tend to leave the anode. The anode would therefore corrode and the cathode would remain intact. It turns out that for pipelines, a power supply has to be used to maintain the system. The sign says 13A.
https://en.wikipedia.org/wiki/Cathodic_protection
