Now mega collector Arthur Moses provides us with a look at that very ad. As you can see, Houdini published the statement in English, French, German and Russian. It's interesting that Houdini seems more roiled about Miss Undina's advertising (which appeared in Das Programm No. 551) than the act itself. It's also interesting that Houdini characterizes the USD as an "escape from a foot pillory under water".
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Ironically, Miss Undina's advertising, which Houdini took such pains to surpress, survives to this day. As you can see, it does indeed borrow from Houdini's own USD posters of the time.
Thank you Arthur. Undina poster image from Houdini's Fabulous Magic by Walter B. Gibson and Morris N. Young.
UPDATE: Miss Undina in color.