Insignias are the way to get Hero Points quickly. The best way is to establish a pattern that allows you to work towards multiple insignias at once. So, for each guard you CQC slam them, hold them up, headshot them, and Fulton them while also not using recovery items, killing anyone, or getting caught, then you're working towards seven different insignias. And each insignia will be worth with three ranks which will total probably around 50,000 Hero Points once you've gotten them all. Granted it takes time.

Another somewhat fast way is if you can find a location where you can get -- for example - six soldiers in one AP recruit session, you can string together a good CQC combo on them. Every combo above two adds another 30 hero points (i.e., 3-combos for 30 pts, 4-combos for 60 pts, and so on). Plus if you have the dress or whatever camo it is that adds 30% Hero Points you can improve that.

Just find that AP recruiting spot, do that mission, go back to home and change the date on your PSP by two days and do it all over again. Tedious but if you find a good spot you can milk a decent amount of hero points faster than if you just did most normal missions over and over.