create a generic hanging sign feature and

move basic_signs' hanging wooden sign back to here, use it.

api.lua

@@ -611,6 +611,14 @@ function signs_lib.check_for_pole(pos, pointed_thing)
 	end
 end
 
+function signs_lib.check_for_ceiling(pointed_thing)
+	if pointed_thing.above.x == pointed_thing.under.x
+	  and pointed_thing.above.z == pointed_thing.under.z
+	  and pointed_thing.above.y < pointed_thing.under.y then
+		return true
+	end
+end
+
 function signs_lib.after_place_node(pos, placer, itemstack, pointed_thing, locked)
 	local playername = placer:get_player_name()
 	local def = minetest.registered_items[itemstack:get_name()]
@@ -622,6 +630,10 @@ function signs_lib.after_place_node(pos, placer, itemstack, pointed_thing, locke
 	if (def.allow_onpole ~= false) and signs_lib.check_for_pole(pos, pointed_thing) then
 		local node = minetest.get_node(pos)
 		minetest.swap_node(pos, {name = itemstack:get_name().."_onpole", param2 = node.param2})
+	elseif def.allow_hanging and signs_lib.check_for_ceiling(pointed_thing) then
+		local newparam2 = minetest.dir_to_facedir(placer:get_look_dir())
+		local node = minetest.get_node(pos)
+		minetest.swap_node(pos, {name = itemstack:get_name().."_hanging", param2 = newparam2})
 	end
 	if locked then
 		local meta = minetest.get_meta(pos)
@@ -711,13 +723,13 @@ function signs_lib.register_sign(name, rdef)
 	end
 
 	def.paramtype           = rdef.paramtype           or "light"
-	def.paramtype2          = rdef.paramtype2          or "wallmounted"
 	def.drawtype            = rdef.drawtype            or "mesh"
 	def.mesh                = rdef.mesh                or "signs_lib_standard_wall_sign.obj"
 	def.wield_image         = rdef.wield_image         or def.inventory_image
 	def.drop                = rdef.drop                or name
 	def.sounds              = rdef.sounds              or signs_lib.standard_wood_sign_sounds
 	def.on_rotate           = rdef.on_rotate           or signs_lib.wallmounted_rotate
+	def.paramtype2          = rdef.paramtype2          or "wallmounted"
 
 	if rdef.on_rotate then
 		def.on_rotate = rdef.on_rotate
@@ -780,6 +792,29 @@ function signs_lib.register_sign(name, rdef)
 		minetest.register_node(":"..name.."_onpole", opdef)
 		table.insert(signs_lib.lbm_restore_nodes, name.."_onpole")
 	end
+
+	if rdef.allow_hanging then
+
+		local hdef = table.copy(def)
+		hdef.paramtype2 = "facedir"
+
+		hdef.selection_box = rdef.selection_box or signs_lib.make_selection_boxes(35, 32, false, 0, 3, -18.5, true)
+		hdef.node_box = rdef.node_box or rdef.selection_box or hdef.selection_box
+
+		hdef.groups.not_in_creative_inventory = 1
+		hdef.tiles[3] = "signs_lib_hangers.png"
+		hdef.mesh = string.gsub(hdef.mesh, ".obj$", "_hanging.obj")
+		hdef.on_rotate = nil
+
+		if hdef.entity_info then
+			hdef.entity_info.mesh = string.gsub(hdef.entity_info.mesh, ".obj$", "_hanging.obj")
+			hdef.entity_info.yaw = signs_lib.standard_yaw
+		end
+
+		minetest.register_node(":"..name.."_hanging", hdef)
+		table.insert(signs_lib.lbm_restore_nodes, name.."_hanging")
+	end
+
 end
 
 -- restore signs' text after /clearobjects and the like, the next time

models/signs_lib_standard_wall_sign_entity_hanging.obj

@@ -0,0 +1,15 @@
+# Blender v2.79 (sub 0) OBJ File: 'basic_signs wooden hanging sign.blend'
+# www.blender.org
+o Plane
+v 0.406250 -0.281250 -0.042969
+v -0.406250 -0.281250 -0.042969
+v 0.406250 0.281250 -0.042969
+v -0.406250 0.281250 -0.042969
+vt 0.000000 0.000000
+vt 1.000000 0.000000
+vt 1.000000 1.000000
+vt 0.000000 1.000000
+vn 0.0000 -0.0000 -1.0000
+g Plane_Plane_None
+s off
+f 1/1/1 2/2/1 4/3/1 3/4/1

models/signs_lib_standard_wall_sign_hanging.obj

@@ -0,0 +1,62 @@
+# Blender v2.79 (sub 0) OBJ File: 'basic_signs wooden hanging sign.blend'
+# www.blender.org
+o Cube
+v 0.437500 -0.312500 0.031250
+v 0.437500 -0.312500 -0.031250
+v 0.437500 0.312500 0.031250
+v 0.437500 0.312500 -0.031250
+v -0.437500 -0.312500 0.031250
+v -0.437500 -0.312500 -0.031250
+v -0.437500 0.312500 0.031250
+v -0.437500 0.312500 -0.031250
+v 0.437500 -0.312500 0.031250
+v 0.437500 -0.312500 -0.031250
+v 0.437500 0.312500 0.031250
+v 0.437500 0.312500 -0.031250
+v -0.437500 -0.312500 0.031250
+v -0.437500 -0.312500 -0.031250
+v -0.437500 0.312500 0.031250
+v -0.437500 0.312500 -0.031250
+v 0.500000 0.312500 -0.000000
+v 0.500000 0.500000 0.000000
+v -0.500000 0.312500 -0.000000
+v -0.500000 0.500000 0.000000
+vt 0.468750 0.812500
+vt 0.031250 0.812500
+vt 0.031250 0.187500
+vt 0.468750 0.187500
+vt 0.531250 0.812500
+vt 0.968750 0.812500
+vt 0.968750 0.187500
+vt 0.531250 0.187500
+vt 0.234375 0.000000
+vt 0.234375 1.000000
+vt 0.015625 1.000000
+vt 0.015625 -0.000000
+vt 0.609375 -0.000000
+vt 0.609375 1.000000
+vt 0.390625 1.000000
+vt 0.390625 -0.000000
+vt 0.765625 0.000000
+vt 0.765625 1.000000
+vt 1.000000 0.812500
+vt 1.000000 1.000000
+vt 0.000000 1.000000
+vt -0.000000 0.812500
+vn 0.0000 0.0000 -1.0000
+vn 0.0000 -0.0000 1.0000
+vn 0.0000 -1.0000 0.0000
+vn 0.0000 1.0000 0.0000
+vn 1.0000 -0.0000 0.0000
+vn -1.0000 -0.0000 0.0000
+g Cube_Cube_front-back
+s off
+f 8/1/1 4/2/1 2/3/1 6/4/1
+f 3/5/2 7/6/2 5/7/2 1/8/2
+g Cube_Cube_edges
+f 13/9/3 14/10/3 10/11/3 9/12/3
+f 11/13/4 12/14/4 16/15/4 15/16/4
+f 11/13/5 9/17/5 10/18/5 12/14/5
+f 13/9/6 15/16/6 16/15/6 14/10/6
+g Cube_Cube_hangers
+f 19/19/1 20/20/1 18/21/1 17/22/1

standard_signs.lua

@@ -7,7 +7,8 @@ signs_lib.register_sign("default:sign_wall_wood", {
 		"signs_lib_sign_wall_wooden.png",
 		"signs_lib_sign_wall_wooden_edges.png",
 	},
-	entity_info = "standard"
+	entity_info = "standard",
+	allow_hanging = true,
 })
 
 signs_lib.register_sign("default:sign_wall_steel", {
@@ -23,6 +24,12 @@ signs_lib.register_sign("default:sign_wall_steel", {
 	entity_info = "standard"
 })
 
+minetest.register_alias("signs:sign_hanging", "default:sign_wall_wood_hanging")
+minetest.register_alias("basic_signs:hanging_sign", "default:sign_wall_wood_hanging")
+
+table.insert(signs_lib.lbm_restore_nodes, "signs:sign_hanging")
+table.insert(signs_lib.lbm_restore_nodes, "basic_signs:hanging_sign")
+
 -- insert the old wood sign-on-fencepost into signs_lib's conversion LBM
 
 table.insert(signs_lib.old_fenceposts_with_signs, "signs:sign_post")