Only by going and searching for my posts to a particular thread in a particular forum. Sometimes, people will reply to something I've said or done on my profile page, and that helps.
In another Internet community where I participate, there's a tracking page where you can see the threads listed where you commented, and there's a clickable link to new comments. Because the whole thing is in (reverse) chronological order with the newest entries on top, it's very easy to check on new stuff.
