(Italian: “label”).  A piece of paper or parchment painted illusionistically, often as though attached to a wall in a painting. Cartellini (pl.)  commonly contain the artist’s name and/or information about the identity of a portrait subject.

Giovanni Bellini. Portrait of Doge Leonardo Loredan (det.). Oil on panel. 1501-02. National Gallery, London. The cartellino contains the artist’s name in Latin.