don't let explosions destroy sign entities

display_api/display.lua

@@ -81,9 +81,16 @@ end
 -- Detect rotation restriction
 local rotation_restricted = nil
 minetest.register_entity('display_api:dummy_entity', {
-	collisionbox = { 0, 0, 0, 0, 0, 0 },
-	visual = "upright_sprite",
-	textures = {} })
+	initial_properties = {
+		collisionbox = {0, 0, 0, 0, 0, 0},
+		visual = "upright_sprite",
+		is_visible = false,
+		textures = {"blank.png"}
+	},
+	on_blast = function(self, damage)
+		return false, false, {}
+	end,
+})
 
 function display_api.is_rotation_restricted()
 	if rotation_restricted == nil then
@@ -304,13 +311,18 @@ end
 function display_api.register_display_entity(entity_name)
 	if not minetest.registered_entities[entity_name] then
 		minetest.register_entity(':'..entity_name, {
-			collisionbox = { 0, 0, 0, 0, 0, 0 },
-			visual = "upright_sprite",
-			textures = {},
+			initial_properties = {
+				collisionbox = {0, 0, 0, 0, 0, 0},
+				visual = "upright_sprite",
+				textures = {},
+			},
 			on_activate = display_api.on_activate,
 			get_staticdata = function(self)
 				return minetest.serialize({ nodepos = self.nodepos })
 			end,
+			on_blast = function(self, damage)
+				return false, false, {}
+			end,
 		})
 	end
 end

signs/compatibility.lua

@@ -61,9 +61,11 @@ minetest.register_lbm({ name = "signs:conpatibility_1",
 -- We need to have this entity registered to be able to remove it.
 if minetest.registered_entities["signs:text"] == nil then
 	minetest.register_entity("signs:text", {
-		collisionbox = { 0, 0, 0, 0, 0, 0 },
-		visual = "upright_sprite",
-		textures = {},
+		on_activate = function(self)
+			if self.object then
+				self.object:remove()
+			end
+		end
 	})
 end