Perhaps I can close the mystery as "SOLVED".
I did a web serch on the last name "Zabik" It turns out it is a common name. A 1940 census of one Zabik family was in Hamtramck, MI a neighborhood in Detroit, MI. Detroit is also the home of John Milligan the famed exhibition slingshot shooter and the maker of the slingshot. Under a magnifying glass I studied the Zabik stamping. The stamping is a fantastic example of single letter stamping I've seen. You can see that certain letters are deeper struck than others and letters not exactly perpendicular to a base line the way a manufacture's stamp would be.
Having experienced a few dog and pony shows as a kid back in the 50's it was common for a professional to show up, performs amazing tricks and then offer to sell goods after the demonstration. One I remember very well was Duncan yoyo's. A pro showed up at school lunch time and on the grounds performed an incredible yoyo act and claimed he would be back the next day with yoyo's to sale. I begged a quarter off of my mother to buy one.
Perhaps this slingshot was purchased at one of Milligan's expos or other source and stamped with the buyers name. As Flatband suggested I am convinced that the stamping on this slingshot is a previous owner's name.
Thanks for everyone's interest and comments.