You must complete the I-20 and Travel Authorization Request form online. Their immigration advisor will send an updated I-20, complete with travel signature, within 3-5 business days.
During the final 2 weeks of each term, the Kearney International Center is available for on-the-spot travel signatures. You must bring your Form I-20 to the KIC during business hours and request the signature at the KIC front desk.
You must receive the signature before you depart the United States.