↑ “XOXO where did x and o come from?”. Hugkiss.com.2011年7月12日時点のオリジナルよりアーカイブ。2022年8月1日閲覧。“The custom goes back to the early Christian era, when a cross mark or "X" was the same as a sworn oath. The cross referred to the cross of Calvary and the first letter of the Greek word for Christ, Xristos.”