According to Spaceflight Now's article Top secret ‘Zuma’ mission puzzles satellite trackers, SpaceX's mission patch for the Zuma Falcon 9 mission is that shown below (and in the article).
I noticed the four-leafed clover at the bottom, then doing a search I've found that this [appears frequently but not always in SpaceX mission patches.
Is there any known or announced significance for it, beyond a general hope for good luck? Why would it appear on some patches and not others?
Alas, as far as I can see, no trace of Zuma.