How do I add this special character to user input?

I found this in a script but don't know what to replace instead of "GuiService"

--		-- CHatHotKey is '/'
--		GuiService:AddSpecialKey(Enum.SpecialKey.ChatHotkey)
--		GuiService.SpecialKeyPressed:connect(function(key) 
--			if key == Enum.SpecialKey.ChatHotkey then 

So I want to add that "/" character instead of this:

mouse.KeyDown:connect(function (key) -- Run function
	if key == "e" then

GuiService is inaccessible to scripts created by users. If you're trying to detect keyboard input, I'd put a LocalScript inside of StarterGui with this code-

wait()
local plr = Game:GetService("Players").LocalPlayer
local mouse = plr:GetMouse()

mouse.KeyDown:connect(function(key)
	print(plr.Name .. " pressed " .. key)
	if key == "e" then
		-- code
	end
end)

mouse.KeyDown:connect(function(Key)
	if key:byte() == 37 then -- 37 is the number code for "/"

You can find more number codes here: http://wiki.roblox.com/index.php/Taking_keyboard_input