"请保持安静。"

Translation: Please keep quiet.

[PeaceJoyPancakes]

"Quiet, please." (On a sign, for example.)

[NasuSamaruk0]

Yes, that is also acceptable.

[MicahLiuba1]

Cannot "please be quiet" do?

[Bjorn605462]

I tried the same, rejected. Hope a native Chinese speaker could comment on this.