A B737-400 WAS PARKED ON THE GATE WHEN THE CREW THINKING THE WHEELS WERE CHOCKED RELEASED THE BRAKES ALLOWING THE ACFT TO ROLL FORWARD STRIKING A TUG INCURRING DAMAGE TO THE RADOME.

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TAXIED TO STOP AT GATE; SET PARKING BRAKE AND SHUT DOWN ENGS. COMPLETED COCKPIT POSTFLT SHUTDOWN PROCS. COMPLETED SHUTDOWN CHKLIST AND RELEASED PARKING BRAKE. ACFT DID NOT MOVE; BUT A SHORT TIME LATER A SCRAPING NOISE WAS HEARD BEHIND INST PANEL. OPENED COCKPIT WINDOW AND ASKED MECH STANDING UNDER JETWAY WHAT WAS GOING ON. HE SAID 'YOU ROLLED FORWARD.' I SAID 'I THOUGHT THE CHOCKS WERE IN;' AND HE SAID 'THEY ARE NOW.' LEFT COCKPIT AFTER RESETTING PARKING BRAKE AND SAW RADOME UNDERSIDE DENTED AND IN CONTACT WITH ROOF OF TUG CAB. I HAD TAKEN A HORIZLY HELD WAND DISPLAYED BY MARSHALLER TO MEAN 'CHOCKS IN.' APPARENTLY THEY WERE NOT. CONTRIBUTING TO MY CONFUSION WAS LOW BLOOD SUGAR. I ATE LUNCH AT XA00 ABC TIME AND WAS SCHEDULED TO EAT ON ABC - ZZZ LEG. INSTEAD TRAINING CREW TOOK FLT AND FO AND I DEADHEADED 3 LEGS TO XYZ. TRAINING CREW ATE MEALS WE WOULD HAVE HAD. WE WERE FINALLY FED ON THE WAY TO ZZZ; 9 HRS AFTER MY LAST MEAL. MARSHALLER STOOD IN FRONT OF ACFT UNDER NOSE INSTEAD OF TO L SIDE OF COCKPIT IN FULL VIEW OF CAPT. FOR WHATEVER REASON; CHOCKS WERE NOT PLACED IN A TIMELY MANNER. A HORIZ MOVEMENT OF MARSHALLER'S WANDS WAS APPARENTLY NOT A 'CHOCKS IN PLACE' SIGNAL; WHICH I TOOK IT TO BE.