Use the profile field manager.
Setup a single selection menu
and in the options box list all 12 one on it's own line.
After you click save, look at the "field##"
Then go into your postbit tempalte and toss this
<div>Sign: $post[field##]</div>
Change the ## to whatever the number is for that field.
Heck you could even do images, but just naming the images EXACTLY what you name the fields even case sensitive and then create a folder named signs off of images. So you'll have..
images/signs/Cancer.gif
etc.
Then in the postbit do
<div><img src="images/signs/$post[field##].gif"></div>
I know it doesn't go off their birthdate and all, but heck, it'll work just the same ;)