Not on this very day in 1941, but by the end of the year (if not a few weeks or months into commercial TV in the U.S.), an early version of the "NBC Test Pattern" below was first inaugurated.
As on this recreation, this was how it looked after the 1947 mods in which the wedge calibration dots were altered in their positions. The first variant of this TP can be found on
this page.
(On the Paley Center's page, they used another repro of the basic TP design.)