Detainees appreciate letters and cards as welcome signs that people in America know they are there and that they care about them. However, keep in mind that all mail to Guantánamo Bay prisoners is censored, and many pieces of mail are not delivered to them. In addition, many prisoners have limited ability to read and understand English. For those reasons, it is best to keep your message brief and simple.
See also Write the Remaining Guantánamo Bay Prisoners for a list of men still there and how to address your card or letter.
Communicate with a Detainee, for sample group letter and group card.