Interesting!!!
 
Invisible RFID Ink Safe For Cattle And People, Company Says
 
 The process developed by Somark involves a geometric array of micro-needles
 and an ink capsule, which is used to 'tattoo' an animal. The ink can be
 detected from 4 feet away.
 

http://www.informationweek.com/software/showArticle.jhtml?articleID=196802844

David Molina