make sure digger is valid before checking for creative

(else assume survival)

README.md

@@ -22,7 +22,7 @@ That said, there are some basic text formatting options:
 
   Writing "^" followed by a letter "a" through "h" will produce double-wide versions of these arrows, in the same order.  These wide arrows occupy 0x89 to 0x91 in the character set.
 
-* A color may be specified in the sign text by using "#" followed by a single hexadcimal digit (0-9 or a-f).  These colors come from the standard Linux/IRC/CGA color set, and are shown in the sign's formspec.  Any color change will remain in effect until changed again, or until the next line break.  Any number of color changes in any arbitrary arrangement is allowed.
+* A color may be specified in the sign text by using "#" followed by a single hexadcimal digit (0-9 or a-f).  These colors come from the standard Linux/IRC/CGA color set, and are shown in the sign's formspec.  Any color change will remain in effect until changed again, or until the next line break.  Any number of color changes in any arbitrary arrangement is allowed. To write "#" on a sign, write "##".
 
 * Most writable signs can display double-wide text by flipping a switch in the sign's formspec.
 

api.lua

@@ -232,7 +232,7 @@ function signs_lib.spawn_entity(pos, texture, glow)
 	end
 
 	if glow ~= "" then
-		obj:set_properties({glow = tonumber(glow * 5))
+		obj:set_properties( {glow = tonumber(glow * 5)} )
 	end
 
 	if yaw then
@@ -555,8 +555,9 @@ local function make_line_texture(line, lineno, pos, line_width, line_height, cwi
 				end
 			end
 			local c = word:sub(i, i)
-			if c == "#" then
+			local c2 = word:sub(i+1, i+1)
-				local cc = tonumber(word:sub(i+1, i+1), 16)
+			if c == "#" and c2 ~= "#" then
+				local cc = tonumber(c2, 16)
 				if cc then
 					i = i + 1
 					cur_color = cc
@@ -707,7 +708,7 @@ end
 
 function signs_lib.rightclick_sign(pos, node, player, itemstack, pointed_thing)
 
-	if not signs_lib.can_modify(pos, player) then return end
+	if not player or not signs_lib.can_modify(pos, player) then return end
 
 	player:get_meta():set_string("signslib:pos", minetest.pos_to_string(pos))
 	minetest.show_formspec(player:get_player_name(), "signs_lib:sign", get_sign_formspec(pos, node.name))
@@ -942,12 +943,14 @@ function signs_lib.register_fence_with_sign()
 end
 
 local use_glow = function(pos, node, puncher, pointed_thing)
-	signs_lib.glow(pos, node, puncher)
+	if puncher then -- if e.g. a machine tries to punch; only a real person should change the lighting
+		signs_lib.glow(pos, node, puncher)
+	end
 	return signs_lib.update_sign(pos)
 end
 
 local glow_drops = function(pos, oldnode, oldmetadata, digger)
-	if minetest.is_creative_enabled(digger:get_player_name()) then
+	if digger and minetest.is_creative_enabled(digger:get_player_name()) then
 		return
 	end
 	local glow = oldmetadata and oldmetadata.fields and oldmetadata.fields.glow