No records exist of what these roadside markings mean, but in the 1920s & 30s, utilities workers would use marks such as these to show were utility supplies were underground. There was no standard and different crews could use different markings – more info here >>>

An extract from the comments reads:
“The note in Industrial Archaeology News, 180 (Spring 2017) on ‘Kerbstone Marks’ reminded me once again of the many fanciful explanations that I have seen regarding the significance or otherwise of such marks. They have nothing whatsoever to do with mason’s marks, nor land ownership, nor pilgrim’s way markers, etc. The truth, certainly for Newcastle upon Tyne, but I suspect also for any area with such marks, is really quite prosaic. They simply indicate the nature of an electrical connection between a main cable, buried in a street, and an adjacent property – coded guides to early supply lines. I have on record about 30 different kerbstone symbols for Newcastle upon Tyne which mainly comprise squares, triangles, arrows, crosses, circles and letters, sometimes in combinations, chiselled into the kerbstone in situ, almost certainly by electricity supply company workers.

In the 1970s I was in communication with a Mr E H Sadler, who had arrived in North East England from London in 1925 to take up a Premium Pupil student apprenticeship – ‘equivalent to a BSc’ – with the Newcastle upon Tyne Electricity Supply Co (NESCO). Mr Sadler would remain in the Newcastle electricity supply industry for the rest of his working life, and was very familiar with the kerbstone marks. In his words:

Cable faults … were common and there was a continuously manned emergency squad of one engineer and three assistants to give ‘fire brigade’ style service to deal with these faults. Location of the actual faults was difficult, and heating of the pavements from the fault current going into the earth was often the quickest and best indication. To help, the position of every joint was marked on the kerbstones of Newcastle.

The commonest kerb mark in Newcastle is a square with a diagonal cross, Saltire style, which simply indicated a ‘joint.’ An added plus sign indicated a joint in the ‘positive’ cable, while an added minus sign indicated a joint in the ‘negative’ cable. The letter ‘F’ indicated a fused connection, and so on. All of these marks probably date from the 1920s and possibly the 1930s.

There is no particular reason to suppose that identical symbols were used elsewhere, for there were no national standards. It was up to individual supply companies to decide to mark their joints on the kerbs, and to determine the design of such marks. The situation in London was bound to be very complicated, for historically it was the most confused district in the country in terms of its electricity supply. By 1917 it had 70 different suppliers, (hence 70 power stations), 50 different types of system, 10 different frequencies, and 20 different voltages; some of these companies would undoubtedly use kerb marks, with their own preferred symbols, while others would not. Hence a possible explanation of ‘long runs – several hundred yards – of uniform kerbstones with no marks’, and hence, no real ‘conundrum’. Newcastle’s situation in the 1920s was much simpler, with only two major supply companies, and far-sighted electrical engineers in the Merz family running the show.

Stafford M Linsley.”