This solution has existed for ages. Let's say I wanted to make a topic on the subject of the comic Prequel. How do I know someone else hasn't posted a topic on it already?

First I go to google.com and type in this (Note: This only works if you can stomach using google for long enough.):
Then these are the search results:

As you can see, the first result shows that someone has talked about it before. I go into the forum thread and check it out. Looks like it is a post that would be better done under Media Discussion, so I do have a reason to go and make a thread there about the comic Prequel if I truly want to.

I then wonder what the second result is. I click on it and read a little, and realized that it is not a topic, but instead is a forum user's bio (I do learn a little bit more about the person though!).

The rest of the results have nothing to do with what I'm looking for, and you can tell this at a glance.

See? How hard was that? Really this stuff is like, Internet 101, but there's a first time for everything when it comes to learning new things. So long as you're willing to fiddle around and experiment, you'll get the hang of it.