I haven't really played the game in years, so I may be missing something. However, I marked a car with the remote control, removed all fuel from fuel inventory + trunk, and added a fuel sensor. This would result in an alert. Clicking on the alert icon opens an "Alert overview" window, where you can use the button on the very left to pin individual alerts below the minimap.
While modding, I always use Creative Mod. If you open its window, click on "Modding" and then "Events", you can select which events it should listen to. I've selected all events, with option "Print events" enabled. Clicking on the pin put me in map view and raised on_player_controller_changed – which is useless for what you want. I could add a handler for on_player_clicked_gps_tag, but I suppose that wouldn't be practical because it would respond to clicks on all GPS tags: If you've got a selected vehicle and accidentally clicked on a GPS tag somewhere in the chat window, the vehicle would try to path there (if it was on the same surface).
