1) The Predator will only attack enemies who are armed in P1 and P2.
2) In P2, the Predator deliberately leaves a pregnant woman alive - despite the fact that she is armed and after him. This is quite obviously one of the biggest indicators that the Predator isn't as clear-cut "evil" as one might think.
3) In both films, the Predator attempts to commit suicide rather than risk defeat at the hands of a human.
4) When Danny Glover successfully defeats a Predator at the end of P2, the rest of the group leaves him alone and alive, even rewarding him with a trophy item. Again, one of the biggest indicators of the code of honor.