Before departing from the US, international students and scholars should visit International Student Services to request a travel signature on their Form I-20 or DS-2019.
Upon port of entry into the United States, Customs and Border Protection officers will check to see if your I-20 or DS-2019 has been signed for travel by an international advisor. Travel signatures are technically valid for 12 months, but it is strongly encouraged by CBP officers to receive a fresh signature each time you leave the US.
Timeline: Plan ahead and request the signature 2 weeks before departure. Same day signatures may not be possible.