What happens if I try to enter the United States without a valid travel signature?

If you arrive at a US port of entry without all the required documents, the customs officer may deny you entry into US. As an alternative, the officer may issue you an I-515A. This document allows you temporary admission into the US. To maintain your nonimmigrant student status, you must submit the required documentation listed on your I-515A to SEVP within 30 days. We recommend that you keep a copy of each document before mailing the original to SEVP.

For complete details please refer to the Department of Homeland Security website.