1. I saw something like this when I watched/read (name of TV programs, title of news article, title of video watched like documentaries)
What I know is

I saw something like this when I watched Pawn Stars.

What I know is that this is a rare sword made to honor heroes in Scotland. There are not many of them, but to ensure that it is an original one, you should contact an expert and what is more take extra care of it.

Explanation:

In this case, we mention a TV show. We relate what we have seen and learned in the tv show with a real life experience where we implement the little knowledge that we have about an object in a situation.

We could have also learned some specific information from a book, video, news article, or any other source. The interesting about what we have learned is that we can implement it in a real situation, no matter where we got the information.