As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUDNED. AFTER TAKEOFF, AIRSPEED RED LINE TAPE STAYED AT 270 KNOTS. CALLED TOMX CONTROL WHO RECOMMENDED RETURN TO DFW. FOUND VMO/MMO SWITCH IN "ALT." SWITCHED TO NORMAL AND SECURED SWITCH GUARD, REF AMM 32-00-00-040-812.