As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LAX-FLIGHT544- AIRCRAFT RETURNED TO FIELD WHEN SHORTLY AFTER TAKEOFF, THE CREW RECEIVED 4 CHIMES AND A RED SMOKE AFT LAV MESSAGE. MAINTENANCE INSPECTED THE AIRCRAFT AND PERFORMED AN OPERATIONAL TEST OF THE AFT LAV SMOKE DETECTOR. OPERATIONAL CHECK WAS GOOD AND NO DISCREPANCIES WERE NOTED. THE AIRCRAFT WAS RETURNED TO SERVICE.