Xox

10 clues
Losing row
Pencil game loser
Tic-tac-toe loser
Certain losing line
Affectionate sign-off
Losing tic-tac-toe line
Noughts-and-crosses line
Worthless tic-tac-toe row
Losing line in tic-tac-toe
Affectionate letters at the end of a letter