Name one of your exhibits accordingly for the desired effect. It should also be noted that if you name a brand new exhibit using this cheat, it will crash the game. Everyone who's done it with a new exhibit has experienced this, so keep it in mind.

Wonderland = More people come
Xanadu = unlock the Unicorn
Doflopnok = Dodo
Cretaceous Corral = Triceratops
Microsoft = Double Exhibit Donations
Blue Fang = Guests pay 2x original amount for attractions

Note: if you name a brand new exhibit using this cheat, it will crash the game. Everyone who's done it with a new exhibit has experienced this, so keep it in mind.