tuesy, I wouldn't use moleskin on a black vintage Singer machine with scrollwork. Those old black machines have a type of finish that is easily damaged, and I would not risk the adhesive on it. I would never put it on a Singer featherweight either, black or otherwise.
At some point the finishes on sewing machines got a lot better, but I'm not sure how far back in "vintage" this happened. I would certainly risk moleskin on some of the newer vintage Singer machines -- maybe on models like the 301, 401, 830, 930; however, I'd probably join a list specific to that kind of vintage machine and ask for advice there first. Some of the people who posts on those lists have amazing technical knowledg of the various models and would know how impervious to damage the finish is.