According to the operator, the pilot performed several practice banner pick-ups in the tailwheel equipped airplane prior to joining the traffic pattern to land. The final approach was uneventful, the tailwheel contacted the runway first, and then the airplane settled onto the runway. During the landing roll, the airplane veered to the right, and the pilot applied full power in an attempt to "fly out of the ground loop." As the airspeed of the airplane increased, it departed the runway, struck a taxiway sign, and came to rest inverted, which resulted in substantial damage to the fuselage. The pilot reported no preimpact mechanical malfunctions or failures with the airplane that would have precluded normal operation.