It's a point his team at Mercedes didn't want him to miss, so on the cool-down lap at the end of the race, his pit crew radioed him the message "default 44" – an instruction that triggered this image to appear on the display in the middle of his steering wheel. Apparently Lewis, with plenty else on his mind (like getting his car back to the parc fermé in one piece and with enough fuel), didn't notice what was flashing in front of him.
Superimposed, as you can see, over an image of Hamilton as a young lad still in karts is Lewis' name alongside those of the other two-time world champs: Jim Clark, Graham Hill, Emerson Fittipaldi, Alberto Ascari, Fernando Alonso and Mika Hakkinen. (Never mind those who've scored more than two titles.) Intriguingly, Hakkinen is the only other one among them to have won either of his titles under Mercedes power like Lewis did, though Fangio won two of his five titles motivated by Benz engines.