In the Dutch journal NRC Handelsblad of November 3, 2020, Ewout Sanders provides background of the phenomenon of singing with an X mark (‘Tekenen bij het kruisje’). He goes back to the 18th century to investigate the meaning of this Dutch expressing of make (or put) one’s mark. He would not be surprised if her history shows that the expression has roots in illiteracy. That assumption seems correct to me and evidence flows from the 17th century story of Rembrandt and his life’s companion at that time, Hendrickje Stoffels. In 1661, Hendrickje gave a testimony about a ‘… drunken surgeon’ (‘een dronken chirurgijn’), who forced everyone who passed him to fight with him (‘… met hem te drincken oft te vechten…’). She attested (‘getuyght’) and signs with a +. In her will from the same year she appoints her child Cornelia van Rhijn (‘haer kindt Cornelia van Rhijn’) as her heir, and Rembrandt, her father (‘desselfs vader’) as guardian. The couple was not married. The notary and the witnesses sign the will. The document states ‘This sign + made by the Testatrix Hendricke (Stoffels)’ (‘Dit teken + gesteld door de Testatrice Hendricke (Stoffels)’. Indeed, it is believed in art-historical literature that she made her mark this way because she was illiterate. The expression therefore has good testimonials in an earlier century.