What was found
PHL TO SDF - DURING INITIAL CLIMB AT ABOUT 500 FT, THE CREW NOTICED A LAV SMOKE MESSAGE DISPLAYED ON EICAS. THE FLIGHT ATTENDANT CHECKED INSIDE THE LAVATORY FOR SMOKE OR ODOR AND REPORTED THAT THERE WAS NO VISIBLE SMOKE OR ODOR. WHILE PREPARING TO RETURN TO PHL, THE EICAS MESSAGE CLEARED AND DID NOT RETURN. THE APPROPRIATE CHECKLISTS WERE RUN IN THE QRH AND THE AIRCRAFT LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED THE ENGINES AND RAN BOTH AT HIGH POWER AND COULD NOT GET THE LAV SMOKE MESSAGE TO RETURN, AND THE AIRCRAFT WAS RETURNED TO SERVICE. THE AIRCRAFT WAS DE-ICED TWICE BEFORE TAKEOFF, THE SECOND TIME APPROXIMATELY TEN MINUTES PRIOR TO TAKEOFF.