Mine was a simple handwritten message, "Rosch was here." I deleted it because I was TTing a lot back then and it filled the board with so many messages.
"I am looking forward to this new journey together!
Also Buck is not a dragon.
Also also...tacos."
To explain a bit, I got a friend into animal crossing at the end of new leaf. So, when they saw Buck in the New Horizon trailer - they thought he was a dragon and we had a huge debate with friends whether he was a dragon or horse lol. Buck ended up as one of my starters. So yup. Tacos are just great...
I posted on my birthday, which was just a little bit after launch. It said something about how I hope the island would grow to be a great place to live. That was the only thing I ever wrote on it. I just don't ever think to put stuff on it, honestly, although I kind of wish I did. Could have written something spooky for Halloween. A thankful message for Turkey Day. But oh well. It is what it is I suppose.