Well-developed chess intuition
All grandmasters have a well-developed chess intuition. That means even without analyzing the position, GMs already know what’s happening on the board, what side is winning and what move each player should play.
That won’t be a 100% accurate analysis, like you will get if you calculate all of the variations or plug in the position into an engine. Nevertheless, it is a fairly accurate evaluation that can be used to make decisions during the game.
Another sign that you have a well-developed chess intuition is ability of guessing GM’s moves during the game. It is very easy to check. Start watching any high level chess game and try guessing what moves one or another player will make. If the percentage of the moves you’ve guessed correctly is high, congratulations, you already may have a well-developed chess intuition.