During the meeting members write notes to each other and stuff them in the rose box. At the end of the meeting a couple people come up and read the notes. Some are cryptic (I'm glad for that as an adviser! )
and others are just plainly worded.
Roses would be for good things, Thorns for bad.
Example (they're pretty lame examples):
Roses to Mary for being elected Panhel President.
Thorns to the electric company when we had a storm last night and I lost my paper.
I've noticed the ones after spring break and the best! and most cryptic!