Those license frames are issued to people that donate at least $1,800 or more to the CHP 11-99 foundation. In return you get a special badge plaque, membership card, and the frame. The saying goes, If you get pulled over by a CHP Officer, they will let you go without giving you a ticket, but you must have the membership card in your possession.
Most of the time you see the frames only on really expensive vehicles. If you see them on a cheap looking car then you know he stole it or bought it from someone.
I have seen them sold on Ebay sometimes for $40 to $80 ....very rare.
Here is the 11-99 foundation link..
http://www.chp11-99.org/index.htm
And link to an article by Stuff....
http://zo-d.com/stuff/automotive/119...orruption.html
And Ebay auction for 1 frame....
http://cgi.ebay.com/ebaymotors/11-99...WDVWQQtcZphoto