In panel 2 there is a portrait on the wall labeled "Ken," which might be an in-joke (Ken Hultgren?).
Signed in the last panel.
Signed "K.H." in the last panel.
Signature in the last panel is consistent with Henning’s signature on his drawing from https://www.fleischerstudios.com/wartime.html (retrieved 1 February 2021). Signature was read as “W. Heusuts“ on Jerry Bails’ Who’s Who.
Signed "Martha Hultgren" in last panel. Martha Eiszner Hultgren was Ken Hultgren's wife, and she wrote or co-wrote most of the stories he drew.