Secret documents cannot be normal steal objectives

code/game/gamemodes/objective.dm

@@ -593,6 +593,8 @@ datum/objective/steal
 			else
 				if(O.flags & 1) // THEFT_FLAG_SPECIAL
 					continue
+			if(O.flags & 2)
+				continue
 			steal_target=O
 			explanation_text = "Steal [O]."
 			return

code/game/gamemodes/steal_items.dm

@@ -3,6 +3,7 @@
 // Separated into datums so we can prevent roles from getting certain objectives.
 
 #define THEFT_FLAG_SPECIAL 1
+#define THEFT_FLAG_UNIQUE 2
 
 /datum/theft_objective
 	var/name=""
@@ -224,6 +225,9 @@ datum/theft_objective/ai/check_special_completion(var/obj/item/device/aicard/C)
 /datum/theft_objective/special
 	flags = THEFT_FLAG_SPECIAL
 
+/datum/theft_objective/unique
+	flags = THEFT_FLAG_UNIQUE
+
 /datum/theft_objective/unique/docs_red
 	name = "the \"Red\" secret documents"
 	typepath = /obj/item/documents/syndicate/red