Some marathons boast glorious histories, others scenic courses. The Little Rock Marathon in Arkansas stands out for its finisher’s medal.

It is the size of a dinner plate and almost three times as heavy as an Olympic gold medal, requiring a team of muscle-bound CrossFit devotees to hand them out. “It’s as big as your head,” says Elizabeth Kalifeh, an Atlanta runner and author of a blog called “Running for Bling.”

The...