Yes, and no.
In Australia, one gets accredited by the National Authority for Interpreters and Translators by either providing evidence of completion of a course of academic study from an institution acceptable to NAATI, or by sitting the translation exam. The exam includes questions on ethics of the profession and one cannot pass the exam if they fail these, no matter how good they are as translators.
Once accredited, you get a seal of office with which you stamp your translations. That plus your signature is all that is required, although I tend to add a few more items to make it look seriously official.
I always translate on my letterhead, starting with the words "Translated from the original/faxed/emailed copy of the Arabic document". I attach the certified copy of the original to the back of my translation, bend the left upper corner of the translation and place my seal firmly on both. This way, the client will know what was translated. The second seal goes underneath the last line of the translated text. Then comes the certification text:
I ___________, NAATI accredited translator Lvl 3 (Professional) hereby certify that the above is a true and correct translation from the Arabic language of [such-and-such a document from such and such a country] relating to [the holder's name].
I then add in the invoice, business card or "With Our Best Compliments" slip, and maybe a brochure on what else we can do for them.
In the USA, on the other hand, things seem to be a tad different. Although the American Translators Association has a program in place that allows members to become CTs, the Overworked Translator (am I envious?) is saying in her post that you do not have to be a CT to produce certified translations.: "In my case, I include my M.A. with my name and indicate that I am an active member of the ATA. You are merely certifying that the translation has been translated “to the best of [your] knowledge and ability.” Any translator can produce a translation which is correct to the best of his or her knowledge and belief."
Sort of a Statutory Declaration. Something like this would be illegal in Australia. There was a court case recently of a Chinese guy who pretended he was an accredited translator, and was jailed for it.