attack, a tack

Attack or attack ( one word ) means to set upon violently, literally or figuratively--
Colonel, we will attack the enemy at dawn.
Do not use this site as a forum to attack other posters.

Attack may also mean an assault, physical or verbal--
He was injured in the attack, and is still in the hospital.
An attack on a man's character isn't a political argument.

A tack or a tack ( two words ) means one ( a ) small nail ( tack )--
Do you have a tack? I want to hang this on the bulletin board.
He put a tack in each corner, so it wouldn't fall down.

Now that you know that, you can say--
"Your son left a tack on the principal's chair, an attack on his person and his office."