A myriad of illegal activity existed in the backrooms of legitimate businesses, where it was but a flower someplace apparent that would clue the seeker what was also going on inside.
Lovers would leave signals for each other, indicating when it was safe or dangerous to proceed.
Samurais would hold mementos, either between their armor or the likeness etched or painted upon it.
There are many, many variations of uses. But what I can tell you definitively is that most, if not all of our symbolic references for flowers used today, grew in part, due to this secret language. There are the obvious allusions that predate the coding of the language, but for the most part Floriography is what boosted these symbolic references into an understood nature.
Anyhow, a chart with one set of meanings is here.
Magnolias and Celandine
A Red Rose
Offered as Lavender
Perhaps, when I get some more time I'll try to simply include the picture of the flower. I did try to do that now, but none of the images would load, so I guess I'll have to figure that aspect out, on how to use downloaded images.