Digitally add a smiley face to Darth Vader’s helmet.
It could look like someone randomly placed a sticker on his helmet in a random angle and he never noticed.
Add a bumper sticker to the back of Vader’s TIE.
“My other ship is a SSD”
After his conversation with Palpatine about how the son of Skywalker lives, he adds a boy stick figure to the man and woman stick figures. After realising Luke has a sister, he adds a girl stick figure as well.