The Secret Service will happily tell you about security features of currency, and behind closed doors help you build methods to detect counterfeits if you have a reasonable justification.
http://www.secretservice.gov/know_your_money.shtml
</pedantry>
http://www.dhs.gov/department-components
The Secret Service will happily tell you about security features of currency, and behind closed doors help you build methods to detect counterfeits if you have a reasonable justification.
http://www.secretservice.gov/know_your_money.shtml