The Note was left with the Lookout when LeChuck kidnapped Elaine Marley and took her to Monkey Island in his Ghost Ship.
It read:
Your Governor is alive and well and by my side as she was always meant to be. If you try to find us you will meet with horrifying disaster. Yours truly, Captain LeChuck.
Acquisition
It was given to Guybrush Threepwood by the Lookout when he completed his Three Trials.
Usage
Threepwood showed it to people about Mêlée Island in order to try and recruit them to his crew.