This is what I came up with:
I used these chalk pins to write "2014-15 First Grade" on the letter.
I stapled the ribbon (from my scrap bin) to back. Lastly, I had all of the kids in the class sign it. Lucky for me, they line up outside the school every morning before the bell rings, so I had lots of opportunities to collect signatures. A few kids still need to sign it, and they'll have a chance after the kids and I present it to her tomorrow.