It is a slippery slope. Singer actually lost the rights to their name for a good while because a "singer" was sononymous with sewing machine much like "coke" is to soda or kleenex to tissues. They regained it in the 40s and repatented several things including the name Singer.
Believe me we've spent hours doing research on the copyrights and patents and trademarks held by Singer for this very reason. It appears that they have reissued their copyrights and granted license to individuals for certain things like the lady who sells manuals, but we haven't been able to make the right contacts yet at Singer for this issue. We have already got the right materials to produce the waterslide decals, and we're doing original work for now but we would like to be able to restore machines to their original condition if a customer wants that, or make the decals available for the DIY restorers out there. So far that has been a no-go because we really don't want to get a cease and desist letter from Singer.