The urge to tell posterity “I was here” runs through art from Jackson Pollock, who allegedly hid a giant signature in one of his most famous abstract paintings, right back to Jan van Eyck, the grandfather of oil painting. His masterpiece, The Arnolfini Portrait, contains an elaborate Latin signature on the wall behind the couple, "Jan van Eyck was here 1434", while in the mirror above, two tiny figures, discernible only with a magnifying glass, stand in the position of the artist looking at the scene, one of them – generally presumed to be van Eyck himself – raising his hand in greeting to viewers down the ages