1 green box: 0-99 reputation points
2 green boxes: 100-199 reputation points
3 green boxes: 200-299 reputation points
4 green boxes: 300-399 reputation points
5 green boxes: 400-499 reputation points
6 green boxes: 500-699 reputation points
7 green boxes: 700-899 reputation points
8 green boxes: 900-1099 reputation points
9 green boxes: 1100-1299 reputation points
10 green boxes: 1300-1499 reputation points
11 green boxes: 1500 reputation points and above
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In terms of titles, it seems to be:
0 or below: Neutral (up to 6 red boxes at least)
1-500: Noted
501-1000: Reliable
1001-1500: Trustworthy
1501-2500: Commended
2501-3500: Renowned
3501-5000: Honored
5001-7500: Hero of the People
7501-10000: Consecrated
10001 and up: Champion of Stormreach
ADDED post 2010: The Epic (guesstimate ~25,000)
ADDED post 2010: The Legendary (hit at 50,000, per Memnir)
ADDED post 2010: Completionist (guesstimate ~100,000)