Keeping a Tally/Count for Events?

I have a certain gameplay mechanic in mind that I would like to implement effectively. Essentially, whenever the player encounters a certain event in the game (sees something happened, is chased by the AI, or even picks up items) I want to keep a tally and have my AI become more aggressive with the increase of the count/tally. I’m not looking for someone to hash out an entire BluePrint for me, but I’d like to know what the best approach for this would be? I was thinking of possibly a “Score/Points” system for the player. I’m just completely lost on how to even begin this.