1) each class gets there own skin not a massive difference but a noticeable one to help aid players to finding certain classes, this would be helpfull when in tournaments etc.
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2) next to the players head in-game there is a logo that is faint but noticeable which corresponds to which class they are.
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3) on the minimap instead of team colored arrows to show team mates have their class logo instead.
again these are just some ideas if you dont like them then feel free to say so/how you would improve or change my ideas, thanks.
-snakeven0m