Check the D20 Modern SRD for its Reputation rules, they might work for ya, or they might not. A character gains Reputation from class levels, normally, and it varies with class; i.e. a Charismatic Hero in D20 Modern will gain Reputation at a rate similar to a strong saving throw, if I recall correctly, while a Strong Hero will only gain Reputation at a rate worse than even a weak saving throw. You could assign Reputation bonuses based on class, since some (such as Bards, Sorcerers, and Wizards) are more likely than others to gain a significant reputation than others (Barbarians, Druids, and Monks for instance), while other classes may gain a mediocre Reputation advancement. There's also a feat in D20 Modern that reduces Reputation by 3 points (for folks who want to be inconspicuous), and another feat that increases Reputation by 3 points (for folks who want to be recognized).