As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF OUT OF PHL LAV SMOKE MESSAGE APPEARED ON EICAS. NO SMELL OR SIGHT OF SMOKE IN LAV. AIR TURNBACK INTO PHL AND LANDED WITHOUT INCIDENT. MAINTENANCE CLEANED LAV SMOKE DETECTOR AND PERFORMED OPS CHECK IAW EMB 145 AMM 26-00-00. OPS CHECK OK. NO FAULTS FOUND. ACFT RETURNED TO SERVICE.