Now, yes. The sign is imperfect. ("Ever" should be "every," etc.) And it's not super cute, either.
But its use of affect/effect was correct. It said, "Quiet hours in effect from 11:30 p.m. to 9:00 a.m."
Then someone decided it would be really smart to go around and change all the signs from "effect" to "affect."
"Quiet hours in affect from 11:30 p.m. to 9:00 a.m.?" No. That doesn't make sense.