You've already worked out the order of quality, these just seem to be a quick measure of how good the car is in a particular mode.
For On-Road, Off-Road and Icy Road you can get a better picture by - when starting a race - going to the change vehicle screen to select a car to race. At the bottom of this page, under the car parts, is a "Road Effect" score give as a positive or negative percentage (presumably a performance modifier of sorts)
My rough experience so far is:
- Concentric circles - positive bonus.
- Circle - no bonus.
- Triangle - slight negative bonus.
- X - large negative bonus.
Unfortunately this doesn't help a great deal for the Adv or Rep scores, which I cannot find a better measure for and we can only assume the same rough measures.