Derek Barnstorm, member of BoardMod , has updated the popular SpikeCity YaBB mod... YaBB Zodiac V1.0 for use with YaBB 2.2.3.  Here is an excerpt from Derek's post on BoardMod:

This Mod was oroginally coded by Spikecity for 2.1, all I have done is update it for 2.2.3 - Thanks to Spikecity for letting me update it.
 
Link to original Mod: http://www.boardmod.org/yabb/YaBB.pl?board=beta_y2;action=display;num=11 83631387
 
This mod shows the zodiac sign in the users profile (both in view profile as text as in the thread as an icon) if the birth date is filled out.