Place ham in crockpot. Score top of ham in a diamond pattern, optional.
Drain pineapple juice into a medium bowl. Measure out 1/4 cup cherry juice. Add to pineapple juice. Whisk in brown sugar and ground mustard. Set aside.
Cover top and sides of ham with pineapple rings. Using a toothpick secure a maraschino cherry into hole of pineapple ring. Whisk together the brown sugar/juice mixture and pour over ham.