I have had this one sitting on my work desk for a while, but every time I tried to post it, the scan would be pretty much awful. So with a new scanner, I gave it another shot. The verdict is still not great, but at least it's readable!
Anyway, this Hawkgirl trading card comes from the good people at Post Cereal as part of their Postopia ad campaign. There were 7 cards in the series, one for each member of the Justice League as featured on the cartoon of the same name. The front features the well known piece of stock Bruce Timm-style art of Shayera getting ready to lay the smack down with her mace. The back side of the card features more stock art, and your standard-issue biographical information. Interestingly, there are some changes from her comics origin as part of her cartoon origin -- the use of a "dimensional transport beam" really smacks of Adam Strange and the Zeta Beam more than Katar and Shayera. Another nice touch is Shayera's role as an undercover police officer, which does not explain her uniform, but is a novel change none the less.
This card came to me via my brother, who is always finding oddball stuff like this. Thanks, J!
Sadly, I got this card long after the Postopia.com ceased to exist, so I do not know what entering the code "THANAGAR4" would have generated as part of your "Justice League on-line adventure." Anyone have any information on that?