Cool ad for a toy, 1907. He is standing on a larger version of the item suspended on the string. Not a slingshot, I think, but some sort of proto-yoyo?
PS from 9/26/13: A delightful message from postcard fan informs me (I should have looked this up) that "a diabolo is not a proto-yoyo but a discrete toy (which enjoys enduring popularity with backpackers of the long-beard-and-colourful-pants ilk)." http://en.wikipedia.org/wiki/Diabolo