Letters denoting a sell out

• Sign of a good turnout: Abbr
• Sign of a hit, briefly
• ''No seats today''
• Discount ticket letters
• Packed, for short
• Sold-out box-office sign
• Sign at a sellout
• Certain hotel, for short
• Neil Simon's favorite letters

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
1941, initialism (acronym) for standing room only.