Like Bruce Wayne reacting to the Bat-Signal in the Gotham City skies, the No.27 on the Anfield substitutes' board meant it was time for Divock Origi's latest act of Liverpool heroism on Sunday.
Having watched his side toil against a limited and relegation-threatened Everton at Anfield, by the hour mark, Jurgen Klopp had seen enough.
Frank Lampard's men had done an excellent job of making the 240th Merseyside derby a slog of a spectacle. Time-wasting and play-acting formed the main parts of the Blues agenda as they clung on and frustrated their hosts.
Then, the hour mark and the changes that would turn the game. On came Origi and Luis Diaz to steer the match in the favor of the home side against their most fierce of local rivals.
Within two minutes, the trick had worked. First, Origi held up a pass from Mohamed Salah before supplying his team-mate with a lay-off that allowed him to cross for, of all players, Andy Robertson.
And then came Origi's moment. One that was almost inevitable after his arrival.
Meeting Luis Diaz's outrageous bicycle kick at the Kop End, Origi rose highest, just like he did in December 2018, to nod home past Jordan Pickford and seal Everton's fate.
How the Blue half of Merseyside must loathe this unassuming, unflappable striker. It was his sixth goal against them in a Liverpool career that has been potted with a series of genuinely unforgettable moments in between large swathes of ordinary and at times even meandering performances.
"He is a world-class striker," Klopp says, curiously, of a player who is sixth choice for Liverpool. But there is a genuine feeling to the manager's assertions. These were not words that were just plucked from the sky following a decisive contribution.
It was back in October that assistant boss Pep Lijnders paid a similar tribute to the Reds striker, saying:
“Divock is one of the world’s best finishers – and we’ve worked with quite a few, at different clubs! He’s an absolute world-class finisher!"
So it is fair to say that Klopp was not simply reactive when talking up the talents of a player who is still some way down the pecking order at Anfield, despite his regular tormenting of Everton.
“He is a legend on and off the pitch," Klopp said. "He is a fantastic footballer for me, and I know it sounds ridiculous as I don’t line him up often, he is a world-class striker, he is our best finisher, definitely."
Origi will be determined to sign off in style at Liverpool
Liverpool were expecting offers to arrive for Origi last summer and were shocked when they didn't. The club anticipated suitors to be lining up to enquire about a Belgium international striker who was available for a move and were instead happy to keep him around as the pursuit on all fronts began.
Origi will never be the first choice at Liverpool and for all the highs he has experienced, particularly since late 2018, he is not a credible long-term replacement for someone like Mohamed Salah or Sadio Mane. Or even, Diogo Jota, whose 21 goals is the best return of his top-flight career this term.
But still, the feeling persists that this enigmatic and seemingly carefree centre-forward has enough ice left in the veins for one more decisive contribution between now and the end of the campaign.
It could arrive in any of the three competitions Liverpool are still competing in and it is why Origi's sporadic Liverpool career - one that has veered from unsuccessful loan spells in Germany to the scoring of winning goals in Champions League finals - could yet still have one last chapter to write.
With a contract into its final weeks at Anfield and interest from Italy persisting, Origi's swansong is now officially underway. But, as he has proven in recent years, do not ever write him off.
And if that No.27 is flashed up on a substitutes' board at some point between now and the end of this thrilling campaign, there could yet be more history to write about.