Some A++ trolling going on at the entrance to Gamescom this year. pic.twitter.com/yXBOZAaPBJ
— Aoife Wilson (@AoifeLockhart) August 16, 2016
Spotted by Eurogamer, the poster doesn't actually read "Half-Life 3", but rather, "Half-Life: 3" and under that in smaller text "Editors Who Played It Back Then". So, the the three refers to the number of editors!
— Kristin Knillmann (@kristinthefox) August 16, 2016