Tagging a user with the styleid

[JonnyQuest]

Question for you hackers:
I need to be able to tag a new registration with the styleid that they are currently using. A cobrand of ours needs to share this info.
I plan on adding a field to the user table (unless anyone has a better idea), however, the styleid is not stored in the URL. Can someone explain to me how to get this out of the session?

$session[styleid]