Detail from the Arnolfini Portrait - Jan van Eyck, 1434
From the National Gallery of Art’s website:
The ornate Latin signature translates as ‘Jan van Eyck was here 1434’. The similarity to modern graffiti is not accidental. Van Eyck often inscribed his pictures in a witty way. The mirror reflects two figures in the doorway. One may be the painter himself. Arnolfini raises his right hand as he faces them, perhaps as a greeting.