Fortunately Leonard Cohen can't sing either and he still manages to pen some great songs, designed to make even one-note Pavarottis sound pretty competent.
My current personal best is Tonight Will Be Fine, particularly this Teddy Thompson version. I nail that sucker, you should hear me in the shower. Teddy and me, we're practically indistinguishable.
Check out the video, pretend it's me singing, maybe brush up on your Spanish (or is that Portuguese?) at the same time, and then please come back and tell me about your signature song.
Do you have a party piece that you wow them with?