A travel signature is required by the USCIS on your I-20 or DS-2019 form anytime that you leave the U.S. (even if you are just crossing the boarder to go to Mexico or Canada). The USCIS prefers a new travel signature if the current signature is older than six months. A travel signature can only be given by a Designated School Official (DSO).
There are two DSOs at the International Center who are authorized by the USCIS to sign documents. Bring your I-20 or DS-2019 form to the International Center at least one week before traveling outside the U.S. to request a travel signature.
If you have applied for Permanent Residency in the U.S. it may not be advisable for you to travel because you may not be allowed to re-enter the U.S. Meet with an International Student Advisor to discuss your immigration status before you travel.