There is now a counterpetition available here on the subject Frank blogged about here and here. The counterpetition speaks for itself, and I will not recreate its points here. It urges that the APA continue its long-standing practice of accepting ads (without any special derogatory mark, either) from institutions that ask their faculty to refrain from homosexual acts. I urge all philosophers who agree with the counterpetition to sign it.
The counterpetition now has signatures from well-known philosophers such as Alvin Plantinga, Alasdair MacIntyre, Jay Budziszewski, and William Lane Craig. (I can attest to personal communication with Alvin Plantinga and Jay Budziszewski about the petition in which they stated that they signed it. Anyone who wishes to allege fraud in any of these cases, as one commentator at Brian Leiter's blog has done, is welcome to make contact with the philosophers in question and ask them if their signatures are genuine.)
Signatures are not limited to APA members but only to professional philosophers. The petition states, "All professional philosophers, including those affiliated with academic institutions or think tanks, independent scholars, and graduate students, are invited to sign." So if you possess a publication record or an institutional affiliation in Philosophy (including graduate student affiliation), you are a philosopher on this definition, even if you are not an APA member. If you are definitely not a philosopher, it would be better for you not to sign. Please, however, do pass on the information to any philosophers you believe will sign.
A word on anonymous signatures: I myself know or have been able to infer from personal communication who several of the "anonymous" signatories are. It is not correct simply to subtract these as if they did not exist; these are real individuals. My own very strong preference would be for people to sign with actual names (and institutional affiliation, if you have one) rather than as "anonymous." I understand however that vulnerable people in the profession are (ahem) concerned about professional reprisals from those who set up the original petition. If you insist on "signing" as "anonymous," I ask at least that you a) put information about yourself making it clear that you are a real person in philosophy in the comments section, and b) consider stepping forward and identifying yourself later since it is alleged that anonymous signatories are mere sock puppets and not real, separate, people.