Porting updates related to material datums. (#12317)

* Porting updates related to material datums.

* art_type

* oh oh

code/game/objects/structures/signs/_signs.dm

@@ -36,6 +36,7 @@
 								 "<span class='notice'>You unfasten [src].</span>")
 			var/obj/item/sign_backing/SB = new (get_turf(user))
 			SB.icon_state = icon_state
+			SB.set_custom_materials(custom_materials) //This is here so picture frames and wooden things don't get messed up.
 			SB.sign_path = type
 			SB.setDir(dir)
 			qdel(src)

code/game/objects/structures/signs/signs_plaques.dm

@@ -46,3 +46,4 @@
 	name = "Mr. Deempisi portrait"
 	desc = "Under the painting a plaque reads: 'While the meat grinder may not have spared you, fear not. Not one part of you has gone to waste... You were delicious.'"
 	icon_state = "monkey_painting"
+	custom_materials = list(/datum/material/wood = 2000) //The same as /obj/structure/sign/picture_frame

code/game/objects/structures/signs/signs_warning.dm

@@ -73,3 +73,8 @@
 	name = "\improper ENGINEERING SAFETY"
 	desc = "A sign detailing the various safety protocols when working on-site to ensure a safe shift."
 	icon_state = "safety"
+
+/obj/structure/sign/warning/explosives
+	name = "\improper HIGH EXPLOSIVES sign"
+	desc = "A warning sign which reads 'HIGH EXPLOSIVES'."
+	icon_state = "explosives"