My first thought was the March 11 attacks on the trains in Madrid in 2004, but why would Djokovic me marking that on his shoes at a tournament in Monaco.
So my second thought is this:
Angel Number 311, or 311 Numerology, represents growth, change, and transformation. 311 is the number of development in every area of your life, including but not limited to relationships, work and career, health, spirituality, personal finances, happiness, creativity, and freedom of expression.
https://subconsciousservant.com/angel-n ... expression.
And since it's Djokovic I'm guessing it's the second one.