Boy's Radium Wrist Watch
Originally uploaded by Ape Lad.
From wikipedia:
Radium was formerly used in self-luminous paints for watches, nuclear panels, aircraft switches, clocks, and instrument dials. More than 100 former watch dial painters who used their lips to shape the paintbrush died from the radiation. Soon afterward, the adverse effects of radioactivity became widely known.
I found this ad in a stack of old Sunday comics. It's dated Oct 3, 1926 and you can see the rest on flickr, including this one (a detail of Polly and her Pals by Cliff Sterrett, one o my heroes of yore):
