In the State of Mississippi, if the electronic ballots are down or your county doesn't do electronic ballots, you are required to darken the bubble next to the candidate you wish to vote for with a Number Two Pencil, usually tied to the small table behind the screen. Tied and packing taped and pretty sure they'd chain the sucker if they could.
You don't get your sticker if you walk off with the Pencil. Those ladies get Quite Upset about it.

Anything other than the darkened bubble is a spoiled ballot.
(If someone can't write for accessibility reasons or can't read, a poll worker goes with them and does the reading and writing for them. They're under oath to be completely impartial.)