A long time ago, when I was in college, I remember my professor discussing Ancient Mesopotamian art and culture. In that lecture, she stated that when you see an upside down flower next to a person it meant that they were meant to be understood as deceased. It was a particular flower, and I can't for the life of me remember, but I've been fascinated by the idea ever since. Can't shake the memory. Any help would be appreciated. Thank you!
Potentially the fleur-de-lis? Inverting symbols is common in art to have them take on an opposite meaning. This website makes the argument that the inverted fleur-de-lis symbol (which could also be a stylised lotus, given the equation of the lotus with ideas of power/life/creation) represents the underworld. It does seem a little dubious as an academic source, but his research and bibliography look pretty solid, and there are a ton of images that might at least jog your memory?
I'm currently at work but I have a couple of books on nature iconography at home that I can take a look at - will edit if I find anything more concrete :)