Types of Negotiable Instruments

On a sheet of paper, Elle writes, without her signature, “I acknowledge that I owe Frank $600, payable out of the proceeds of the sale of my car, a 2003 Honda Civic, which I promise to advertise ‘For Sale’ next week. Payment is to be made on or before six months from today.” What type of instrument is this? Is it nego¬tiable? If not, why not?