I wish auction houses would do a bit more research before exposing their descriptions. The following is a great postcard, but Hake's logic that it dates to 1904, based on the Chicago Union Giants having become the Leland Giants by 1905, is just wrong. I have only researched a limited time period, but the Union Giants were right there in Chicago with the rest of the black city teams, 1909-1912.
http://www.hakes.com/item.asp?Auction=204&ItemNo=107036