Eamonn O Brien
I think the important part to remember is what capacity you act in in relation to the person at the time of signing...
You could include on the invoice...
On the x day of x I signed a promissory note and gave it to your bank for lodgement. I am now seeking the return of said note or the value thereof as all contractual obligations have been met.
State your capacity when signing the invoice... Something like that... :D