Where and how to sign a painting is a subject that comes up regularly on the
Painting Forum, but one question I've not yet heard is what to do if your name is so long it won't fit on a painting very easily. That's a problem which occurred to me when I discovered what Picasso's full name was. How's this for a mouthful:
Pablo, Digo, Jose, Francisco de Paula, Juan Nepomuceno, Maria de los Remedios, Cipriano, dela Santisima Trinidad, Ruiz Picasso
His name was apparently in keeping with local tradition, and he experimented with various shortened versions and even circled initials before setting on "Pablo Picasso". Today we generally hear him referred to as simply "Picasso". (I found this bit of art trivia flicking through a a fascinating in a rather heavy-weight book called
A Sum of Destructions: Picasso's Cultures and the Creation of Cubism, on page p209.)
Where, How and Why to add a Signature
Make someone's birthday extra special by creating a unique card or other handmade item for them. Here are some ideas from across About.com's Hobbies sites:

"Whatever [other artists] have is something needed to do their work -- it wouldn't help you in your work even if you had it. Their magic is theirs. You don't lack it. You don't need it.
"What you need to know about the next [painting] is contained in the last piece. ... Ask your work what it needs, not what you need."
-- Art & Fear, pp34-6.
If learning to ask your painting what it needs sound a tad like pop-psychology for you, put it into art speak: learn to critique your own paintings. To critique it honestly, bluntly, but also constructively.
Image © Marion Boddy-Evans. Licensed to About.com, Inc