Blackfriar Anti-Climb Paint, Black, H&M T Shirt. 
Edition of 4. 
Thanks to Andy Richardson, Damon Rostron, Robin Smart.
Photo credits: Laura Dee Milnes and Artist's own. 

"Finally, and this may or may not happen, but I mentioned yesterday about wanting to put something up high in the space, and that it might be these version of the ‘s’ symbol. I wanted to paint something using anti-vandal paint, as in all respects it’s like other oil paint, it just never dries, and is made solely for that purpose. It’s black and shiny, like the obsidian mirrors, and I find it funny because it’s used to stop people breaking into places but like the glass on walls, is actually illegal to do so without providing warning of its presence, and has to be installed over a certain height. 

The ’s’ doesn’t seem to have an origin, but there are loads of apocryphal sources/stories out there; seems to be one of those spontaneously generated symbols of no ownership, often used in graffiti (alleyways again, school books, desks, bored youth, doodles,etc) and resembled the shape made when I was hand-lapping (grinding) the glass iphones. Repetitive action, easily reproduced. Also, it bears a resemblance to a mathematical curve, like the roof of the school next door, and makes whatever it touches untouchable."