In this thread, after post 45. Something with a blue background, no attribution, no post number. I haven’t noticed one of those before.
I think it might be a staff notice. It appears to be an option we mods have that we haven’t used before.
I’ll try adding one to your post.
I kind of like it, might be good for housekeeping stuff like thread moves & merges.
FYI - I have used it before.
I should have said, “that I haven’t noticed before”.
I also mentioned it in the newbie moderator’s guide.
(Yes, I’m just giving you a hard time for no reason now…) 
Hey look at that:
If desired, you can also add a Staff Notice to the post being moderated. This is useful in bringing attention to a particular mod note so that other users will know that the post was moderated.
That paragraph never registered before with me. Now I know what it means too.
BTW: Thank you again for the guide. It was invaluable at first.
But later on it became a burden. A crushing burden that ate away at your very soul.
I love this place.
Me too.