The Department of Homeland Security screens foreign citizens who want to live and work in the United States to ensure that they are not a threat to U.S. citizens. The U.S. Citizenship and Immigration Services explains that after you complete immigration documentation such as a request, petition or application and file it, officials use your biometrics to positively identify you. The biometrics appointment is when you provide proof of your identification.
Any information you provide to the USCIS must be completely true, and you will be required to confirm this at your appointment. Since the digital signature, photograph and fingerprints you provide will be used to run extensive background checks in many databases, false information could have a devastating effect on your application.
Your signature verifies that the facts you provided in your documents were accurate and complete when you filed them, and that you have checked it for errors. Therefore, if you are over the age of 13, you must provide your signature or mark unless there is proof that a mental or physical disability prevents you from being able to fulfill this requirement. An inability to write, whether in your native language or in English, does not exclude you from this condition.
You will need to bring your passport, Green Card or other official document with photo identification to your appointment. Since the USCIS does not provide copies of documents, you may want to make copies of all paperwork for your own records before you submit it. This information may give you an idea of what to expect from your biometrics appointment, but it is for educational purposes only and should not be considered legal advice.