Ahem, there are no less than three examples in the wikipedia page you're trying to cite that back me up:

and cases where the circumstances were held to show no larceny: R. v. Wood (1848) 3 Cox C. C. 277 (banknote found on open land) R. v. Dixon (1855) 7 Cox C. C. 35, 25 L. J. M. C. 39 (lost note without mark) R. v. Shea (1856) 7 Cox C. C. 147; R. v. Christopher (1858) Bell C. C. 27, 169 E. R. 1153 (unmarked notes and purse found in public place)

I used a $50 bill (which is implied to be unmarked) purposefully.