I have to thank my Flickr friend Glen Mullaly for solving this mystery for me.
What's really bizarre is that I had initially posted an "A.S." illustration and another piece clearly signed "Arthur Sarnoff" together back on Father's Day and never made the connection. Doh!
I found quite a lot of artwork and information on Arthur Sarnoff at various websites. There's a bit of biographical info at askart.com. The American Art Archives has a tremendous selection of Sarnoff illustrations (including several wonderful Karo Kid ads). And you can see some of Sarnoff's later work (and even buy one of his originals) at The Illustrated Gallery.
For those who are fans of pinup art, there's a baker's dozen of fresh, hot lovelies by Sarnoff at the Virtual Pin-ups Art Gallery.
Another weird coincidence: the very day I posted about the mysterious "A.S.", I received the scan above from Ranger Bob asking if I could make out the signature at the bottom left. I tell ya, its like the spirit of Arthur Sarnoff was trying to guide me in the right direction....
All of the images above (and all the "A.S." illustrations previously seen here) are now in my Arthur Sarnoff Flickr set where you can view them at full size.