Green’s Dictionary of Slang

anything for which one cannot specify the proper name.

1894		Dly Independent (Helena, MT) 31 Mar. n.p.: They turned a whole raft of con motos and scherzos and op. 27’s and appoggiaturas and other chromatic dingbats loose on him.
1905		L. Pound ‘Dialect Speech in Nebraska’ in DN III:i 66: Indefinite expression applied to something, the name of which is not readily recalled [...] dingbat.
1912		J. London Smoke Bellew Pt 7 🌐 ‘Well, gosh-dash my dingbats, if you haven’t beaten me to it,’ Carson swore whimsically.
1917		O.O. McIntyre New York Day by Day 20 June [synd. col.] So I greased the dingbat. And we started up again.
1927		Capricorn (Rockhampton, Qld) 27 Oct. 8/4: ‘Thundering dingbats,’ exclaimed the drover.
1947		B. Rose 15 May [synd. col.] I don’t think any wire-and-glass dingbat [i.e., television set] is going to ‘oontz’ out cheek-to-cheek dancing [W&F].
1981		G.V. Higgins Rat on Fire (1982) 64: She’s up the K-Mart sellin’ dingbats to dingbats or something.
1989		H. Rawson Dict. of Invective (1991) 117: dingbat. Serving as a general word for any item whose true name is not known or which is not to be mentioned (such as the male genitalia, for instance).