Possible Clues:

• "Quiet!," rudely
• "Pipe down!"
• A1: "___ already! Sheesh."
• 'Silence!'
• ''Shh!''
• 'Shut your trap!' ... and, graphically, what the circled letters do
• "Shut your trap!" ... and, graphically, what the circled letters do
• How to make the letter V valid?
• 'Lighten up!'