In a footrace, a course official rings a bell as the lead runner begins his or her final lap of the track. A gun is used to signal the start, not the beginning of the end, of a race. But Dr. Ink finds a teachable moment here, beyond the uses of feigned humility.
Cliches often lose their original denotations.
The second version suggests a person towing a rope connected to a heavy weight. The original may have preceded the Marquis of Queensbury rules of boxing when a fighter had to toe a line in the middle of the ring to indicate he was fit to fight another round. In the 1960s I worked in a city room with a fair number of World War II and Korean War veterans. They clearly saw the PR guy's job as throwing up flak against an approaching squadron of inquiring reporters. The term struck me as a direct metaphor for anti-aircraft fire.