To add to Jim's post, I would caution you about marking a product "patent pending" if you in fact know that it is not patentable (e.g., you know of invalidating prior art). 35 U.S.C. 292 imposes stiff penalties on parties who improperly mark their products "patent pending" for the purpose of deceiving the public.
That said, it is far safer from a marking perspective to assume that any application supporting a "patent pending" mark claims and contains patentable subject matter.
35 U.S.C. 292:
Whoever, without the consent of the patentee, marks upon, or affixes to, or uses in advertising in connection with anything made, used, offered for sale, or sold by such person within the United States, or imported by the person into the United States, the name or any imitation of the name of the patentee, the patent number, or the words "patent," "patentee," or the like, with the intent of counterfeiting or imitating the mark of the patentee, or of deceiving the public and inducing them to believe that the thing was made, offered for sale, sold, or imported into the United States by or with the consent of the patentee; or Whoever marks upon, or affixes to, or uses in advertising in connection with any unpatented article the word "patent" or any word or number importing the same is patented, for the purpose of deceiving the public; or Whoever marks upon, or affixes to, or uses in advertising in connection with any article the words "patent applied for," "patent pending," or any word importing that an application for patent has been made, when no application for patent has been made, or if made, is not pending, for the purpose of deceiving the public - Shall be fined not more than $500 for every such offense.