This is Beaver's Mystic ball, which he uses to make decisions. It is based on the mystic '8' ball which is very popular in America. Watch Friends, and you find one sitting permanently on Chandler's office desk. It has also been consulted in Seinfeld, Toy Story and The Simpsons.The idea is that the mystic ball, doubles as two things. An executive paperweight and a soothsayer.
Thanks to Marilyn Scott-Waters for suggesting the idea - her original design can be found here.
This jpeg is A4 size so can be printed out and made up.