Little tip, Mike Windu, despite it being far from my place to give one. Don't be a fictional character. Don't be 'Will Turner'. Be yourself. Write something that is from your pen, your heart, and not the pen of some scriptwritter somewhere. You will get much more respect and love from your girlfriend if the signature is yours, the line is yours. Otherwise you might as well buy a commercial 'Pirates of the Caribbean' themed Valentine card.
Trust me, it will work. Enjoy.