Formerly there were only so many underground "assets" as they now seem to be called. Not so long ago, all there can have been under the streets were water mains, drains and sewers, nearly all municipally owned under road surfaces maintained by the highway authority, in our case Leeds City Council. In that fairly stable situation I can see how permanent signs on the surface came into use.
More and more was crammed in there, and some of it was the responsibility of regional or national public utilities. The Public Utilities Street Works Act 1950 was enacted to deal with this but the local highway authority remained in overall charge. They employed "PUSWA" inspectors who went round, well, inspecting and they sprayed the once-familiar corner marks on the bits that needed reinstatement after being dug up.
Privatisation of utilities and the introduction of cable TV etc with digging up just about every street in the land, led to the enactment of the New Roads and Street Works Act 1991, which gave "statutory undertakers" new rights underground and empowered them to do their own reinstatement. Whatever the benefits, there were some problems such as roads being nicely resurfaced and contractors arriving to dig them up before the tarmac had set. There's also been the perennial problem of the JCB digging down and biting off more than it was supposed to chew. There was a telly ad intended to reassure us that there was some sort of co-ordination of all the digging which ended with a traditional undertaker looking as though he too might make use of an excavation.
The paintmarks are, of course, short term and they eventually wash off. The fact that a whole street may be surveyed using the methods described in my link suggests to me that over the years, we've rather lost track of what's down there. The reason I'm surprised that there seems to be no definitive set of rules for the markings used suggests to me - as a complete layman - that there's the possibility of confusion. Instead of it all being done by local authority people who might easily have stayed in the same city for their entire working life, specialist contractors in one type of utility might work anywhere, deciphering the marks left by others.
A couple of years ago, the whole of Finkle Lane in Gildersome was surveyed and colourfully marked like this prior to a new electricity cable being laid. I rather enjoyed looking down at everything when the road was dug up and I used to show my grandchildren so I didn't look quite so daft. "There's a hole and we are looking into it."