Hills Bank made slogan buttons from at least 2008 to 2019. In 2015 they made buttons for home and away games, but in general they only made home and bowl games. They did not make buttons in 2012, according to a collector. The buttons were black, except in 2011 when they were yellow. In 2018 the buttons featured throwback logos and in 2019 they featured famous Iowa alumni.
Iowa has also made Homecoming buttons since the mid-1920s. Penn State traveled to Iowa for their homecoming on four occasions, all of which have buttons: 1930, 2001, and 2010. The University catalogs these buttons here.
I got my Iowa Hills Bank and Homecoming buttons from the kind people at Hawktoys, you should check out their collection for all your Iowa memorabilia needs!
Hills Bank
Homecoming
Penn State made anti-Iowa Buttons
We Are "Pin" State 