Early in the 2019 season, Major League Baseball instructed video monitors working in Minute Maid Park to listen for banging sounds emanating from the Astros’ dugout, a person with knowledge of the directive said Monday.

The Astros are alleged to have stolen signs during their World Series-winning season of 2017 using a system that included players banging on trash cans to signal certain pitches. That MLB directed those working at Minute Maid Park to listen for such sounds is an indication the league already had an eye on Houston.

Conversely, a video monitor who worked in another American League ballpark told the Chronicle they were not “implicitly told” to listen for any sounds from either dugout.

MLB began investigating the Astros last week after former Houston pitcher Mike Fiers outlined how the team stole signs in 2017, using a camera in center field and a video screen in the tunnel next to the dugout, then banging on trash cans.

Rumors of the Astros’ tactics — including, but not limited to, banging on trash cans to signal when a specific pitch was coming — had circulated around baseball well before Fiers told The Athletic about the Astros’ system.

Fiers told The Athletic the Astros set up a camera in center field at Minute Maid Park that focused on the opposing catcher. The feed was streamed to a television below the Astros dugout.

Houston players or employees watched to get signs and, when they did, communicated them via a “loud noise,” The Athletic reported. Social media was subsequently filled with videos that all but confirmed the setup — instances when noises were audible moments before certain pitches were thrown.

The Athletic’s report detailed alleged wrongdoing in 2017 only. Whether the Astros continued their practices into 2018 or 2019 remains unconfirmed. Astros general manager Jeff Luhnow said he was “confident that in general, we did things right and we try and follow the rules.”

The team has said it is cooperating with MLB’s investigation.

“Beginning in the 2017 season, numerous clubs expressed general concerns that other clubs were stealing their signs,” MLB said last week. “As a result of those concerns, and after receiving extensive input from the general managers, we issued a revised policy on sign stealing prior to the 2019 season. We also put in place detailed protocols and procedures to provide comfort to clubs that other clubs were not using video during the game to decode and steal signs.”

Part of that revised policy included a group of video monitors at each ballpark responsible for ensuring clubs adhered to the new regulations. Each game last regular season had at least one person around both the home and visiting dugouts monitoring the replay room, clubhouse, tunnel and any other area.

“What they told us was we were essentially looking for people who were using technology to steal signs,” said one video monitor.

One person familiar with the Astros’ video monitoring said those who worked at Minute Maid Park were instructed “early on” to “make sure there was no one in the dugout banging.”

Video monitors are otherwise obligated to ensure that teams follow the revised policy, one that bans the use of electronic devices to identify opposing signs or communicate them to players. Only independent sign stealing — when a runner on second base picks one up, for example — is legal.

On monitors inside the clubhouse or dugout, games can be viewed only on an eight-second delay. The replay room is the lone exception. Any time a player is seen looking at that live feed, a video monitor is compelled to report it to Major League Baseball.

Other infractions that must be reported include any discussions between players, coaches or team officials about a plan to steal signs, any seen video feed from the outfield between the foul poles, and any use of unapproved electronic devices. League-approved tablets are permitted.

Clubs that break these rules are subject to “progressive” discipline, according to a copy of the 2019 policy obtained by the Chronicle. It states that if a team engages in a “premeditated plan to steal an opposing Club’s signs using electronic equipment,” it “in violation of these Regulations with the knowledge of any front office or on-field personnel will result in the loss of player selection rights under Major League Rule 4 or loss of benefits under the International Amateur Talent System.”

Houston’s sign-stealing has drawn the ire of opponents for the last two years. Major League Baseball cleared the Astros of any wrongdoing after accusations during the 2018 postseason, when a camera-wielding employee was removed from the photo well at Fenway Park, concluding the event was surveillance and not spying.

During this year’s American League Championship Series, several unnamed members of the Yankees organization accused the Astros of whistling loudly to convey what pitch was coming. General manager Jeff Luhnow and manager A.J. Hinch vehemently denied the act. MLB found no rules violations.

“I think that when an organization has success, there’s going to naturally be critics trying to figure out things that might not be right or things that that organization may have not done properly,” Luhnow said at last week’s general managers meetings. “We haven’t done everything properly, but I do feel confident that in general, most of the time, we did things right and we try and follow the rules. We try to be good citizens, and we try to compete as hard as we can.”

Luhnow’s organization has been under league investigation since October, when the franchise mishandled reports of offensive language directed at female journalists by assistant general manager Brandon Taubman, who was later fired during the World Series. Fiers’ accusations added another chapter in a calamitous month.

Commissioner Rob Manfred is scheduled to speak Thursday at MLB’s owners meetings in Arlington. During his tenure, he has issued only one public punishment for electronically stealing signs, fining the Red Sox during the 2017 season.

“All 30 Clubs have been notified that future violations of this type will be subject to more serious sanctions,” Manfred said in his 2017 ruling.

chandler.rome@chron.com

twitter.com/chandler_rome