这是从我们学校OISS网站上抄来的,应该对所有F1适用吧
Travel Signature on I-20 or DS-2019 – Make sure your I-20 (for F-1 and F-2 status) or DS-2019 (for J-1 and J-2 status) has been signed in the travel authorization section by an OISS adviser within six months of your expected return to the U.S.
如果你现在在国内,尽快跟你们学校的OISS联系一下,看看能不能把I-20寄给他们,让他们签字后再寄还给你。