These are the same people as carve their names into the rocks and boulders of local landmarks.
The graffiti-ing of summit markers seems pretty commonplace on accessible continental peaks. Have a look at photos of the summit marker on Toubkal.
This post also made me think about the trig points themselves. Most people I know like the things - part of the landscape of the UK uplands, but I'm sure if they didn't exist and some organisation revealed plans to place a white concrete pillar on the top of many significant peaks and tops, well, I know what the response would be.
(Those stone-built trigs are more tasteful, mind you).