The FBI in conjunction with the Bureau of Justice Assistance and Joint Regional Intelligence Center have produced a number of fliers to help the public identify possible terrorists. While some of the points have merit, it is very likely that this will generate an extremely high proportion of false alerts based on perfectly reasonable and legal behaviors.
A big red flag for me were the fliers for cyber cafes and electronics stores. These suggest that the use of privacy protecting services, like Anonymizer, should be deemed suspicious. They also call out Encryption, VoIP, and communicating through video games.
In almost all of the fliers they suggest that wanting to pay cash (legal tender for all debts public and private) is suspicious.
Thanks to Public Intelligence for pulling together PDFs of the documents.