The thumb signal may have originated in ancient Rome, used by Colosseum crowds to pass judgment on conquered gladiators. It may have arisen as a symbol of a done deal in medieval commerce, or it might simply be something we humans aped from the apes.
However its origins, the signal has since proven an effective means of communication -- for World War II air pilots, for road-weary hitchhikers, for Siskel and Ebert.
And here in 2014, it has found new merit and meaning among an unheralded-but-essential class of men in Major League Baseball: Bench coaches.
Instant replay has shined new light on their role and responsibilities, because bench coaches are the ones you'll see on the top step of the dugout. They'll signal to the skipper on the field, via thumbs-up or thumbs-down, whether the play in question ought to be challenged or left alone.
This new arrangement has led, here in the early going, to an awful lot of TV face time for guys whose jobs are often overlooked.
"It's about time we got something going," joked Indians bench coach Brad Mills.
Replay, though, is merely one small aspect of an increasingly sophisticated position in the big league spectrum. In the grand scope of the game's long history, the role is still relatively new. As far back as 1919, when the great Christy Mathewson stuck around post-playing days to sit alongside the legendary John McGraw, it has not been unheard of for a manager to seek assistance of some sort. But "bench coach" was not considered a formal term until the '80s, and it wasn't an assignment on every Major League club until 2013, when Jim Leyland pulled Gene Lamont in from coaching third base.
"Originally, it was just to get another coach to help you do the work," Lamont said. "But it's become more important, probably, now that you've got some younger managers."
Lamont now works with one of the youngest in Brad Ausmus, and the going line on rookie skippers is that they need a veteran presence alongside them to help navigate through the rough and tumbling waters of the 162-game schedule, as well as the pitching changes and clubhouse policework contained therein.
In truth, though, the game has become so stat-conscious, so scrutinized and so savvy that even the most veteran of skippers can use a helping hand.
A manager's responsibilities, after all, extend not just to the clubhouse, but to the many members of a growing media, and his in-game tactics involve not just the decision of when to yank the starter, but where to properly position the defenders using batted-ball data or how to maximize matchups using advanced analytics.
Bench coaches, therefore, have become vital organs in the big league body.
"I think every manager is different in what he needs from his bench coach," said Bud Black, whose former bench coach, Rick Renteria, took over as skipper for the Cubs this year. "But some qualities that are important [across the board] are an in-game component, a strategy-based component and a good pulse of the team, a good rapport with the players."
Renteria, Black said, was adept at handling clubhouse politics, putting out fires that only would have distracted Black from bigger tasks. So while Black, a former pitcher and pitching coach, didn't necessarily need much input from Renteria on the aspect of in-game mound swaps, the off-the-field communication the bilingual Renteria provided was particularly meaningful.
That element is also a significant part of Mills' responsibilities to Terry Francona. The two worked in tandem on two World Series winners, helping Mills eventually land a managerial opportunity in Houston. But when things didn't work out with the Astros, Mills found himself reattached to Francona in Cleveland, where the bench coach could be seen before a recent game taking the mental temperature, so to speak, of several players before batting practice, while Francona handled his daily media briefing.
"There are a lot of demands on a manager's time," Mills said. "You have to make sure all the information is assimilated to the team, to the players. A manager needs to know things are being taken care of the way he'd like them to be taken care of. So I talk to them and see if they're able to take BP, to take ground balls, to help us off the bench. I'm able to give Terry that information, and we go from there."
We are in an increasingly sophisticated era of information, and the growing coaching staffs -- several of which now employ dual hitting coaches and/or defensive coordinators -- are a reflection of this.
For as long as bench coaches have been around, they've functioned as an extra set of eyes on the action, but now they also help incorporate the avalanche of info, too.
"You help them facilitate," Royals bench coach Don Wakamatsu said. "All of it is just the awareness that you bring to each and every single play of the game. Heck, we think about little things like going to the bathroom. You have to time your bathroom run, because you can't miss anything."
That's especially true now that manager challenges have been added to the in-game intrigue. By and large, the bench coach is the one fielding the call from the video coordinator and providing the appropriate signal.
In Cleveland's case, Mills and Francona sat down during Spring Training to go over the signs. Francona asked Mills to give him a thumbs-up if he should challenge, a thumbs-down if he shouldn't, or for inconclusive reviews, a flat hand extended out anywhere from his waist to his head to express the coordinator's degree of confidence in disputing the call.
"Now we look around," Mills said with a laugh, "and everybody else is doing the exact same thing. We all came up with the same signs!"
Indeed, like the bench coach role itself, the thumb signal has become commonplace on the Major League scene.
Anthony Castrovince is a reporter for MLB.com. Read his columns and follow him on Twitter at @Castrovince.