UPDATE: Maury pointed out that a porcelain sign of this badge sold in 2017 (see bottom).
In the April of 1946 issue of the Saturday Evening Post (same month in Colliers, too), Willys-Overland introduced a new advertising badge for the Willys engine.
As you can see in the introduction ad (A New Chapter), it was matched with the announcement of the Willys-Overland Jeep Station Wagon, though the ad hides the wagon in anticipation of its summer of 1946 launch.
The badge made a second appearance within the release-announcement of the station wagon in the August 18, 1946, issue of the Saturday Evening Post.
The next month, in September of 1946, the badge appears for a third time, again associated with the wagon.
As quickly as the badge appeared, it disappeared with the same speed. For the October 1946 ad, which included a wagon in it, the Saturday Evening Post seemingly replaced the engine badge with a smaller badge, one with a “W” over the “O”. It’s the earliest jeep ad I can find with that badge (if anyone knows of another, earlier ad, please let me know).
At some point, there was a porcelain version of the sign. One sold on eBay in 2017:
