This is what it says regarding rearward facing seats. Funny how it says "should not" and not a definite "NO!".
WTF do you think should means ?
It's an auxiliary verb used to indicate duty.
Can not, implies an inability. ie. incorrect because you can.
Will not, implies a willingness obviously by your desire incorrect.
Thus "should not" is correct as is "must not".
I don't care if people get grammar wrong cos I am fucking useless at grammar, but don't go round correcting people. Yes that is hypocritical of me, but it fucking annoys me when people correct me with incorrect grammar. (ie. I didn't start the fire!)