Well, it depends on your definition of 'passenger.' Say there's 4 people in a jeep, do you only want the person next to the driver to get the message, or do you want everyone to get the message? If you only want the person next to the driver to get the message, then isObject(%mounted=%veh.getMountedObject(1))?%mounted.client:0 will work just fine, but if you want them all to get it, you're gonna have to loop through each slot and do the same check for that slot #.