As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHORTLY AFTER TAKE OFF, LAV SMOKE EICAS MESSAGE APPEARED AND RECEIVED WORD FROM FLIGHT ATTENDANT THAT SHE SAW SMOKE AROUND THE FLOOR BUT NONE COMING FROM THE LAVATORY. NOTIFIED ATC OF THE SITUATION AND RETURNED TO FIELD AFTER PERFORMING QRH PROCEDURE.