Jacob (JT Neal) receives a letter from "UNL", which is the University of Nebraska-Lincoln.
UNL (the University of Nebraska-Lincoln) is part of the University of Nebraska system. Campuses are located in Lincoln (UNL), Omaha (UNO), Kearney (UNK), and the University of Nebraska Medical Center (UNMC).
When Jacob (JT Neal) shouts "I'm going to be a Husker!", he is referring to the Cornhuskers (shortened to Huskers), the mascot for the University of Nebraska.