The idea of using a duplicate item with an ambiguous signature to stand in temporarily for an item genuinely signed or initialed by a spectator, usually in the context of an object-to-impossible-location effect, was used to avoid using a slide in the coin-to-match-box trick. This idea is described under the title of “Slide-less” in The Phoenix, No. 5, Apr. 3, 1942, p. 18. The author—Ann Y. Mous, a punning pseudonym, probably Bruce Elliott—opens by stating the idea appeared in the “forgotten files” of an old magic magazine. The original source has so far eluded discovery. The coin was initialed by a spectator.

Karl Fulves, in Rigmarole, No. 9, 1994, p. 10, writes that John Scarne used a duplicate card with a dummy signature that a spectator found in an envelope in his pocket, before Scarne switched it for a (forced) duplicate that had been signed by another spectator. Fulves does not date Scarne's performances of this variant of the Western Union Card Trick, titled “Remote Control”, but Dai Vernon and Eddie Fields recollected seeing Scarne perform a version of the Western Union Card Trick; see The Vernon Chronicles, Vol. 3, by Stephen Minch, 1989, pp. 208-212. This would likely have been sometime from the 1940s to the 1960s.