How do I mark feeds in Google Reader as new?

I am trying to use Reader on my blackberry, but it will only show the feeds that are marked “new”. Unfortunately, when accessing Google Reader on the regular web, I can’t figure out how to mark a particular feed as “new”. All I’ve been able to find is that supposedly “M” is a keyboard shortcut to mark/unmark as read.. but that doesn’t actually seem to work, in practice. Any ideas?