The AT forum software automatically adds the REMOVE into your email address in your profile if you make it visible.
Adding any sort of nonsense to your email address will help to some degree in preventing spam. People use REMOVE or something like that in order to make it obvious to actual humans that the word needs to be taken out in order to get the real email address. The way it prevents spam is that many spammers using software bots to read through pages on forums and websites looking for email addresses. If they find your address with REMOVE added, they'll try to send email directly to that adress including REMOVE, so it won't ever get to you.
Of course it's not foolproof, as a spammer could write a bot which knows that any email addresses coming from for example AT which have REMOVE in them, the bot needs to strip that out to get the actual address. But at least you prevent the spam from the ones that don't bother to do that.
Another way some people try to foil spammers is writing their address with spaces in it, like "me @ domain.com", or in such ways as "meATdomain.com" or similar. Again it works to varying degrees, but at least hinders the spammers who don't put a little more effort into it.
If your email address is anywhere online, no matter how you try to obfuscate it, you're going to be likely to get some spam. That's why most people "in the know" use spam-catcher addresses whenever possible, such as a Yahoo or Gmail or Hotmail account, to sign up for forums and stuff (like when you have to register to download software). If like AT you can't use certain mail providers, many ISPs provide 5 or even more email addresses for every account, so you can just make a spamcatcher address that way. Of course with any spamcatcher that you use to sign up for something that could result in you getting legitimate email, you have to monitor the account anyway. That's why 3rd party spam filters are popular.