Adds an option to enable/disable markings on synth parts.

-In char setup near the synth color option.
-Tested working although the preview icon may misbehave with the icon cache. (Meaning the effect will require refreshing the cached icon with a visual change, such as color, markings, limb status change, etc. to show up, and may not show up at all if the appearance is identical to an earlier one already saved to cache and getting loaded from there instead of refreshing.)

code/modules/organs/organ_icon.dm

@@ -179,6 +179,14 @@ var/global/list/limb_icon_cache = list()
 	if(model)
 		icon_cache_key += "_model_[model]"
 		apply_colouration(mob_icon)
+		if(owner && owner.synth_markings)
+			for(var/M in markings)
+				var/datum/sprite_accessory/marking/mark_style = markings[M]["datum"]
+				var/icon/mark_s = new/icon("icon" = mark_style.icon, "icon_state" = "[mark_style.icon_state]-[organ_tag]")
+				mark_s.Blend(markings[M]["color"], ICON_ADD)
+				add_overlay(mark_s) //So when it's not on your body, it has icons
+				mob_icon.Blend(mark_s, ICON_OVERLAY) //So when it's on your body, it has icons
+				icon_cache_key += "[M][markings[M]["color"]]"
 
 	dir = EAST
 	icon = mob_icon