Each Stadium has a stamp that you can get. Usually its at Guest Services and they usually have something to stamp it on if you dont have anything, but there is a leather bound Passport book you can buy, but at $89.99 its a little pricey. I found out about these after my stadium quest started but I have most of them and will continue to get them. On an interesting note, I saw a game at Yankee stadium in the Bronx, NY and Fenway Park in Boston on the SAME DAY which might be rare. Notice both stamps have the same date of June 11th, 2019.
