Make an appointment to see an ISA in T.2500 at least one full week before you depart Minnesota. In some cases, the ISA will need to endorse your I-20 on p.3 so that you can reenter the U.S.; in others it may be necessary to prepare a new I-20 for you. The signature is typically good for one year of travel, unless you have graduated and are on post-completion practical training, in which case it is only valid for 6 months.
The I-20 should be signed each time you leave the U.S. and want to reenter. Every F-1 student or F-2 dependent will need to present these documents to reenter the U.S.: