I stumbled upon a thread made by Angelo here: http://www.urban-rivals.com/community/forum/?mode=viewsubject&forum_page=0&id_subject=1929468&subject_page=0
He is offering a bonus in exchange for cards that were created earlier. If I understand correctly, if you go into your collection and click on a card to go to it's character page you will see a series of numbers in the url after the '&id_pj=%XXXX-xx' The lower the first series of numbers, the older the card. The second series of numbers appears to be the clan id. Cards with codes of 4 numbers or less are extremely rare! You should see Angelo's thread above if you happen to possess one.
So I was wondering UR, what is your oldest card? To find out, simply go to your collection, find the 'Sort: By Clan' and select it to be 'By date'. Click the first card that comes up and report back with your findings!
Mine is Copper with 232084558, a ten digit code! Not so lucky, but it's pretty cool finding.