LINCOLN, Neb. — Sometimes younger fans enter the Best of Big Red store near Nebraska’s campus and ask the owner, Mike Osborne, why, amid all the Cornhuskers apparel and tchotchkes — earrings and garden gnomes and beer cozies that look like corncobs — there is a football helmet in a glass case with one side painted in Nebraska’s colors and the other in Oklahoma’s.

“Old-timers like me look at it and get it,” said Osborne, 51, a lanky, soft-spoken man who gives off a Mr. Rogers vibe. “Others are like, ‘Why do you have an Oklahoma helmet?’”

The helmet is a silent reminder of one of college football’s great rivalries — one now dormant, and one whose passion might take some explaining to fans under 40. It has been six years since the last meeting between Nebraska and Oklahoma and decades since their annual game was a rite of fall that merited the entire nation’s attention, regularly holding in the balance a conference title, an Orange Bowl berth and, quite a few times, a national title.

And while the helmet is Osborne’s favorite item in his store, it is also a reminder that the best of Big Red may be history. The most marketable thing about Nebraska is probably its past.