Back in the preseason, when the Bears were still getting to know new defensive coordinator Chuck Pagano, safety Eddie Jackson had a confusing interaction with him after practice.

Pagano walked up and told him good job for an interception, then shook his hand. Jackson felt something crinkle in his palm and looked down in disbelief. Did his coach just give him a $100 handshake? He was nervous — “Is this legal?” — but also a little delighted.

Jackson wasn’t stunned for long. When he opened the paper, it was, in fact, a $100 bill. But the face in the center wasn’t Benjamin Franklin. It was Pagano.

“Cool prank, Chuck,” he retorted as both men walked away laughing.

And that was how a new currency began circulating Halas Hall: Chuckbucks.

You’ll find lots of things strewn about at locker stalls. Players leave shoes and watches worth more than your car, hard-to-pronounce nutritional supplements and an array of gear. But never cash.

So it was unusual to see another safety, Ha Ha Clinton-Dix, proudly holding up a Chuckbuck to show off to anyone nearby. Then he rummaged in a cabinet in his locker and pulled out a stack of at least 20.

“You’ve gotta earn these, man,” he said. “They don’t just come out of nowhere. I love the Chuckbucks. They’re gonna be worth a lot of money one day, so you better get your hands on them. I’m telling you.”

It appears the only way to get one, though, is by making a big play. Since coaches aren’t allowed to give out real money — what a perfect week for this to surface, by the way, with the Saints coming to town Sunday — Pagano wanted a way to convey the sentiment.

Jackson believes Pagano printed out the Chuckbucks on his own, possibly from his computer.

They aren’t close enough to actually be confused with money, but it resembles it sufficiently that Jackson wasn’t the only player fooled by them for a moment.

“The first one he gave me, I thought it was some cash,” Clinton-Dix admitted sheepishly. Like Jackson, he quickly shot back at Pagano, “ ‘OK, Coach. I’m gonna go to the restaurant with all these Chuckbucks and tell them I left my wallet at home.’ ”

Pagano, the former Colts head coach, has been guarded with the media since his hiring and clearly meant for this to stay as an inside joke. He seemed less than pleased that media discovered it and wouldn’t explain how the reward system works.

“I just can’t give you that secret,” he said. “I’d be telling too much. It’s kind of a deal that’s just in our room. I don’t know how that got out. You must have seen that money floating around.

“Don’t try and cash the Chuckbucks. You’re not getting anything for them.”

Try telling that to Clinton-Dix. He joked — maybe — that he’s going to hang on to them as an investment. Pagano acknowledged the value could go up with inflation.

“I told those guys, if you want me to sign it, I’ll sign it,” he said. “And I said don’t spend it, because it’ll be [worth] $105 when I die. Things go up a little bit, so I think it’ll be worth $105.”

It’s a long, grueling season, and little things like this help liven life up for players, but Chuckbucks are more meaningful than they might appear at first. It’s a way for Pagano to show respect.

Consider that Clinton-Dix is making $3 million in salary and still treasures his Chuckbucks.

“Chuck is one of the most open coaches I’ve ever been around as far as being a people person,” he said. “He’s a cool dude. It’s the thought that counts.”

That’s heartfelt.

“And,” he added, “maybe it’ll turn into something later on, so I’ll hold on to them.”

Sun-Times reporter Patrick Finley contributed to this story.