I made such signature the first day I got my FP. And yesterday, someone told me this signature intrigued him, so he went to look on the website. Now he’s subscribed for a FP2 
Just a tip: put one or two enters in your signature. Otherwise, the text will be too close to your actual message.
My signature reads:
>>Sent from my FairPhone - www.fairphone.com
Oh, and I think the idea was also spoken about in this topic