Question - Workers Markers and Their Meanings

[Caver]

I was down a drain today in the bottom end of a system which has no graffiti just the plain concrete walls of the tubes. I don't think anyone is ever down there as it floods even with minor rain. At the beginning is a Y junction and on the way out I noticed the letters SG written in capitals in yellow writing about 10cm high.

This got me thinking what markings do the workers use and what do they all mean?

 

[The Lone Ranger]

The majority of these marks are from inspections; some are just distance markers, some highlight defects while other markers are just photo identifications.

If you inspect a drain you may end up with lots of photos which once you come out all look the same, plus they may inspect a couple of drains in a day, photo ID's makes life a lot easier once you get back to the office and write the report.

They are also then know points for future inspections to either monitor a defect or carry out some maintenance work.