As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON FLIGHT 4378 (GSP TO DTW) AN AIR RETURN WAS PERFORMED DUE TO SMOKE TOILET MESSAGE ON CLIMBOUT OF GSP. AN EMERGENCY WAS DECLARED AFTER FOLLOWING CFR AND THE AIRCRAFT LANDED SAFELY. INSPECTED LAVATORY AND FOUND BURNED OUT BULBS IN RETURN TO SEAT SIGN. REMOVED AND REPLACED LAVATORY RETURN TO SEAT SIGN ASSEMBLY IAM AMM 33-24-04. OPS CHECKS GOOD.