Yes, unfortunately that is the case. This is described as the “booking question exception” to the Miranda warnings. Miranda warnings are a list of rights that you have by way of the US Constitution. The most prominent of these rights are the right to remain silent, and the right to consult an attorney (or have one present while you are being questioned).
When you are arrested, but before you are placed in a jail cell, a booking officer will typically ask you several questions (ranging from whether you have any diseases, to whether you are in a gang). But these booking questions do not have to be preceded by a reading of your Miranda warnings. This is because it is not considered to be the same thing as a typical police interrogation. As a result, any statements you make to the booking officer can and will be used against you in a court of law. (Pennsylvania v. Muniz, U.S. Sup. Ct. 1990).
So if you are being booked at the jailhouse, and the booking officer asks you a routine question about any gang affiliation, your response can be used as evidence. If for instance you say that you are in fact associated with a certain gang that is suspected of criminal activity in a separate matter, the booking officer could be called as a witness to testify as to your affirmative response at a trial. This can happen even though you were not read any Miranda warnings before the question was asked by the booking officer.