It's probably a dummy reminder by mileage that you can set, reset, disable and change the interval of. '11 to '17 Leafs had that but the controls for the dash are TOTALLY different on the '18.
Someone probably enabled it by accident while playing w/the controls.
Looking for a video/reference now.
edit: Found it. D/L the '18 Leaf owner's manual from https://owners.nissanusa.com/nowners/na ... nualsGuide
. See page 2-34 Instruments and controls. There are two Maintenance options: Tire and Other. See page 2-27 for how to operate (and/or watch https://www.youtube.com/watch?v=6DwWyExJc4c
). This is for the display in the instrument cluster, not the stereo or nav system.
On '11 to '17 Leafs w/nav, there were also similar dummy reminders you could set on the nav system that were independent from the gauge cluster's.