Make the marker type "Empty" in the editor. Then at a later time, in a trigger, WP, or script put;
"MarkerName" SetmarkerType "MarkerType"
Where MarkerType can be any of the following;
"Start" =Arrow moving out of a circle
"End"= Circle with an arrow going into it from the top
"Pickup"= Arrow bouncing in and out of a circle
"Empty" = Circle with a diagonal line through it
"Marker"= X icon
"Destroy"= Targetting icon
"Arrow" = Arrow
"Flag1" = Flag icon
"Warning"=Exclamation Mark
"Dot"=Simple little dot. Can use these to denote movement paths
"Join"=Two Arrows joining in a circle
"Unknown"=Question Mark