Letters on a party invitation indicating that booze won't be provided by the host

• P.S. on an invitation
• Part of an invitation to an imbiber
• Invite abbr
• Inits. on a party invitation
• T.G.I.F. party request
• "I'm not providing, you drunks!"
• Letters of invitation?
• Letters on some invitations
• "We're not serving liquor," on invites

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
initialism (acronym) for "bring your own bottle" or "bring your own booze," by 1951.