Hmmm... good question. If you can't look it up on mormon.org, I wouldn't bother. The church is annoying about resigning, and says that it's an ecclesiastical matter that has to be solved with your bishop, but they're just setting up hoops for themselves. Legally, you just send it to member records, and as soon as they receive it, you're out. I haven't resigned, so I'm not the authority on this by any means. Check out this link: http://www.exmormon.org/remove.htm
You could also ask at the forums on postmormon.org.