The BBC have, what I think, is a fascinating article on the signs and symbols spray painted onto the road by utility companies.
Each different colour means something different, as does each line, squiggle, letter, and number. There is no official rule on what each means, but a common language has been built over time. For instance, red spray paint means electricity, and show where electricity cables run. Blue denotes water pipes, whilst yellow refers to gas, and green is a more recent addition, showing showing communication cables (like CCTV networks or cable TV lines). White is the general “sticky notes” of the business; little reminders of what is going on below ground.
It’s an interesting read, and provides a little bit of context when you see these squiggles on the road. Onwards!