I post a sign on the 1st and the 15th the says, "TUITION IS DUE TODAY. THANKS!"
I dont think your sign is rude, but it might be on the long side for someone reading at the door. I usually send home more wordy notes/reminders with each child. Instead, I might put on the door a sign that reads,
"PAYMENTS ARE DUE ON FRIDAY.
$10 PER DAY LATE FEES APPLY.THANKS!"