If you chose “Overseas Employment/Visa”, it should have given you a Standard Disclosure. I suggest contacting AFP to see if they can check your request, they might keep it on file. If you did in fact select “Overseas Employment/Visa”, then the AFP has made a mistake and should hopefully arrange for a proper one to be sent.
I tried to post the image but it just wasn’t showing up, so here is a link to a pic of what the certificate should look like. https://www.dropbox.com/s/epj5714pi2u5l1o/2013-04-21%2011.16.13.jpg
Let me know if the link doesn’t work