The card was sent to a Mr. Hugo Koenig of Watertown.
The back reads:
Hello Hugo -In its early days, Borchert Field was used for far more than just baseball. The field was flooded in wintertime and used as a skating rink. The rink was run by Henry Sperber, who also operated the concessions during baseball season. When Sperber hoisted a white flag with large blue circle up the left field foul pole, neighborhood skaters would know that the ice was ready.
Picture of the Base Ball Park Ice Rink Band - Bleachers in the rear
This is the first I've heard of a brass band to entertain the skaters, but we shouldn't be surprised to see this from the man who ran a bar behind home plate during games (reportedly the best views in the entire park were from his barstools).
In or out of the baseball season, Athletic Park had a long history of providing Milwaukeeans with a pleasant afternoon's entertainment.