There are lots of variations on the legend of the maneki neko cat. There's even an entire maneki neko club with its own website, at http://www.amy.hi-ho.ne.jp/~mono93/cat/english/index_e.html

In a nutshell, you can't buy one for yourself. The raised paw brings money (or good health). If you get one/both, you should take your cat back to Goutokuji. We did. Should have kept hold of him...!