The theme of the present post originated in a fragment of an illustration for a Buick advertisement I noticed in a book. I don't know whether or not the image was cropped (I've failed to locate the original ad on the Internet), but what I have bears no signature.
The man and women pictured in the car have gentle little smiles, an expression that strikes me as being surprisingly rare in advertising. So who painted that illustration? My guess is that it was Barclay. As evidence, I present below several known Barclay illustrations showing people with similar expressions. Furthermore, it is known that Barclay occasionally illustrated Buick advertisements. Let me know whether or not my guess is correct.
This is the unsigned (or cropped out) image and those gentle smiles.