You would take the code from the ticker place that's for the bbCode and place it in the Signature block, not the avatar. Avatars are those little pictures to the left of the message, where your name, location, number of posts to date are.
I just updated and added my ticker to make sure I was getting the details right. I goofed earlier and put the wrong code in the space and was wondering why it wasn't showing. Oops!
Yes, it will automatically update when you change your stats on the ticker site, as long as you use the "update ticker" link instead of making a new ticker each time your weight changes or you want to change graphics.