Are there any security features in US currency that the public doesn’t know about? I know that UV lights bring out some differences in the little strip. I’m not actually thinking of making a buck, and if this poses any legality issues the mods know what to do.
Not to be sarcastic or anything, but if there are security features that we don’t know about… I imagine we wouldn’t know about them.
I found this link to the Bureau of Engraving and Printing, but it doesn’t say much about what actual actions are being taken to fight counterfeiters.
This link has an interactive bill which describes three of the security measures currently in use.
Hope this is along the lines of what you’re looking for.