the marker is pretty easy, place the marker where you want it to appear set the marker type as "empty" so i doesnt show on the map then in the trigger add ; "nameofmarker" setmarkertype "Destroy"
so the activation of the trigger reads "1" objstatus "DONE"; "nameofmarker" setmarkertype "Destroy"
play around with the different types of markers such as
"Flag", "Flag1", "Dot", "Destroy", "Start", "End", "Warning", "Join", "Pickup", "Unknown", "Marker", "Arrow", "Empty".