If you look at trinkets in the gnogging window, you can see that you can have a feat and one reinforcing rune. I spent many weeks trying to get a trinket to drop that had a reinforcing rune on it, to no avail.
Then I noticed that you can craft trinkets in woodcrafting. Once you get some stars for that specific trinket, you will start getting reinforcing runes. It's up to you if you want to spend a socket to add it to another trinket.