If you want readers to subscribe to your RSS feed, it’s a good idea to make the subscription button (or link) prominent. It should definitely be “above the fold”, visible as soon as the page loads in the user’s browser, and visually eye-grabbing.
Taking this to an extreme, there’s a meme going around the web about the “world’s largest” or “world’s biggest” RSS button. This meme has gotten (pleasantly) silly.
I think it started when ReviewMe.com claimed to have the world’s biggest:
Just for the record, mamakk has the smallest RSS button: 1px by 1 px
See it here (if you can =P):