Related Clues:

• "Au revoir," to a Brit
• "Byeee!"
• Indian conglomerate
• Reduplicative "See ya!"
• "See ya," in Sheffield
• "Later, gang!"
• The "TT" of TTFN
• Contradictory signoff on a walkie-talkie (In this answer, note letters 4-7)
• "G'bye!"