So the marker only informs that they have a history/potential to have it. DSU are the ones who are responsible for intially finding the drugs. There's every possibility after stopping and searching the vehicle/passengers using their dogs that they find nothing, which would negate any need for CID in the first place. If we were to add CID to this, there's every possibility they show up for no reason
For this reason, DSU are the only ones to be flagged for a drugs marker, as they pull over and search, if there is something they can then call CID over. It prevents units being needlessly called for a traffic stop.