it seems this is a sort of 'potluck' surveillance technique for the reasons you mentioned. they might have been discovered by a scanning device, after the first one was found I am sure they would continue to look for more incidents.
I could see them useful if an employer was watching employees who deal with cash. till skimming tracking. the contractors may have been accidental recipients.
I see another application where a spouse or equivalent might give you a 'lucky coin' and the words "now don't you spend that"...... "honey, really I went fishing", might not work anymore.
some links: http://www.spychips.com/
RFID defined: http://en.wikipedia.org/wiki/RFID
Your favorite shows are back!
Don’t miss your dramas, sitcoms and reality shows. Find out when and where they’re airing!