I've only seen it spelled "Kash", so I prefer that.
Next time you make a topic, give more information. I was confused for a second until I realized what you meant.
Also, please refrain from making topics like this. By this kind of topic, I mean one with only a four word question
There is a correct way to spell the name of the vault, and obviously people are going to prefer that way of spelling it.
Silly topics are silly.