If you look at google : search on: hide button You see a lot of different hide buttons that you can use. Just rename the button lijke hide.jpg (see wat is named in the file)
go to your admin cp>>Custom BB codes>> BB code manager open it after opening it you will see the hide bb code, edit it and in the image field put the link of your hide image and save it thats all.
If it helps you please click on the thanks button.