An Angel Policy clearly defines whether rubber stamps can be used to create products to sell. It will state whether there are any specific restrictions or limitations.
(Defined from about.com : rubber stamping)

LoriaDesign LLC absolutely support the angel policy.
We use stamps to enhance our creativity, we agree to respect terms and conditions from all angel companies.

Every hand stamped cards will display each company's copyrights on the back of the card and we will make lists of Angel companies that we use on this page.