The beast with five fingers

I noticed this curious phenomenon at work a wee while ago and wondered how on earth they could have got there. I suspected that either the builders or some passers-by had decided to leave their mark while the coating was still drying. but it didn't seem that likely and I kept puzzling about it. Then one lunchtime I passed by while the lunch runners were about to start their run. They were all leaning their hands against the wall doing stretches.

It's obvious now I know.