Other mistake: When Roy and Johnny help free the man whose arm is trapped in the pipe, just as the man stands up we can see the boxes of detergent on the shelf behind him, with their brand names covered with black tape.
Revealing mistake: When Station 51 is dispatched to 'man trapped', just as Engine 51 rolls out of the apparatus bay and heads down the driveway, the real 127's vehicle is seen parked inside the bay, near the rear door.
Continuity mistake: After bringing the man who choked on a beer can's pull tab to Rampart, when Squad 51 returns to the station and backs up the driveway, the engine seen parked in the apparatus bay is the Crown from seasons 1 and 2, not their current Ward LaFrance engine.
Continuity mistake: After examining Tommy, when Brackett speaks to Mrs. Lawson, the boy's mother, her handbag is hanging off her shoulder in all the shots facing Brackett, but in all the shots facing Mrs. Lawson the bag is gone.
Answer: Yes, there's a thin cable secured to the sign's bottom mounting bracket which leads upward to the crane arm, and can be seen in quite a few shots at various angles. It's reasonable to presume that this cable which is secured to the crane was part of the sign's mounting process to the two wall brackets before the winds caused the accident, the premise of this rescue. For this reason it really can't be noted as "stunt wires being visible" or something like that.
Super Grover