The vintage machines had lots of different decals. They changed with the factory that made them and with the years. For example, I have a Sphinx set of decals on my treadle Singer 27. The same machine also came with Pheasant decals. I'm not exactly sure why they changed them, but there are lots of variations. The non-Singer machines usually had decals too. The prettiest (IMHO) were the victorian ones with lots of curly ques. You can find information about the decals on historical machine sites - Needlebar, ISMACs, TreadleOn, and the Smithsonian site.
Pam