On the Weinmann you can try heating the frame with your hair dryer, while its still hot put some masking tape over part of the residue. Make sure it is stuck down tight and carefully lift the tape to pull away the residue left on the bike. You might have to do this several times. For the Nishiki, look for plastic razor blades or a hard plastic scraper. Heat up the decals and use either to scrape them off.

Other products that work:

1.) Naphtha paint thinner.

JR.