I received an e-mail from a Weldon library staffer. It reads, in part:
I have two more of these notes I've found, see attached for photos. Unfortunately I don't have the title or page info where they were found. They're the same format -- wingdings-esque font, special symbol in the code, small item contained in envelope, and larger image in bottom-left. They have the same URL on the back.
I've been totally intrigued by these envelopes, and for a while was considering finding an amateur cryptography message board to share them with. My coworkers, alas, are not quite as thrilled by secret coded messages, and speculate that they were part of a scavenger hunt, but have no other concrete knowledge of the origins of the messages.
I hope this helps you on your search! Keep me updated!
Each of these came with an object as well, but they weren't leaves. Note that different symbols are in colour in these notes, which matches the object in the note.