The 'On' and 'Off' markings near the Parking Brake lever is just like the 'Up' and 'Down" markings near the Landing Gear Lever.
But the calls as mentioned in the Standard Callouts on the FCOMs are 'Set' and 'Released' for the Parking Brakes. When we need to raise or lower the landing gear, we command "Gear Up" or "Gear Down" and not "Up" or "Down". For that matter there is no "Up" , "Down", "On" or "Off" callouts mentioned in the SOP.