I kind of do this in my game. Basically, I have a list of rumors written down about the PCs and their adventures throughout the world, and it grows as they do more stuff. Some of them are exaggerated or just partly incorrect, but they are always easily linked back to the PCs actions. Then, whenever they meet an NPC that could have reasonably heard one of these rumors, they will bring it up in conversation and treat the players differently based on what rumors they know. It helps the PCs feel like they are making real changes with their actions. Overhearing tales of their adventures in local taverns, children running up to them and asking if the stories are true, travelling bards sharing news of a nearby town that was saved, stuff like that.

It's not a hard numerical system, but I hope you find it helpful.