This time, she wrote one word: Yetunde.
Memories of her slain half-sister inspired Williams to a 6-1, 6-2 win over top-seeded Maria Sharapova in the Australian Open final - her eighth Grand Slam title, her first since winning here in 2005, and her most improbable.
"Usually I write, 'Look at the ball, move forward, do this, do that.' Today I just had one word. My note was just 'Yetunde.'
"Every changeover I looked at it and I just thought about how happy she would have been ... about what an amazing sister she was to me. I just said, 'Serena, this has to be more than enough to motivate me.' And I think it was."
Williams used to enjoy talking to her sister after her matches, something that ended abruptly when Yetunde Price was killed in a drive-by shooting in California in September 2003. Working through a series of injuries and the death of her sister took a toll on Williams, and the domination that she and her sister Venus had on women's tennis eroded.
Her championship on Saturday was her first in two years, and only her second in a Grand Slam after completing her "Serena Slam" in Australia in 2003, when she won a fourth consecutive major.
"There's always times where you think, 'Am I ever going to be looking at another trophy?' Especially since I hadn't won a tournament - let alone a Grand Slam - in a long time," she said.
Her win over No. 5 Nadia Petrova - after she was two points from exiting the tournament in the third round here - was her first over a top-10 player since she won the Australian title in 2005. She then beat up-and-comer Jelena Jankovic in consecutive sets and had a tough quarterfinal win over Shahar Peer, before another 2-set win over French Open semifinalist Nicole Vaidisova.
She reserved her best for reigning U.S. Open champion Sharapova, who will assume the No. 1 ranking on Monday and had a 13-match winning streak at Grand Slams going into the final.
Williams is only the second unseeded player to win the Australian title in the Open era.