Taxis in American Samoa are not clearly identified as such. The only way to be sure a car is actually a licensed taxi is to look for a T or TA on the license plate. Drivers are required to have commercial licenses and most are pretty good drivers.
Taxis vary in quality from excellent down to only fair. There are few, if any, taxis on the road in bad condition. Nonetheless, if you have a choice, take the best looking one.
Drivers vary too. There are no meters on taxis. Many drivers are very aggressive with fares and you are always subject to being cheated. There is a fare schedule published here but even the drivers don't often know what those fares are. Ask questions and negotiate with the driver before getting in.
Your hotel can tell you how much fares are to various places. If you are off a tour ship, you might want to ask a police officer or a local resident for help with taxi fares.
You can find numbers for Taxis on our sister site here.