Field tag is a better description as wesb said. The carcass tag is given out when the animal is checked at a check station. Annual license buyers have an area on their license to write in the info for their harvest. I use a business card with my info, then just add date and time of kill.
I have always wondered about this seemingly liberal method of tagging a deer (or other animal) in OK. I grew up hunting in Wisconsin and Minnesota, both states which issue a numbered back tag to hunt deer (a roughly 3" x 8" tag pinned or carried in a tag holder visible on the back shoulder area of each hunter). The lower portion of this tag is perforated and ripped off to attach to your kill. The remaining uper portion of the back tag still has the license info, and the deer is legally tagged with the lower portion of the tag attached.http://www.tagbagstore.com/
There is a cost to produce such tags, especially when they would have to be mailed to ALL lifetime license holders each year. The funny thing is that in many states with such tags, resident hunters complain about the tags and want something different like we have in OK!