I work in an environment where official documents must often be signed by supervisors, executives, etc. I am constantly amazed by the fact that signatures are rarely legible. If someone reading the document didn't already know the signatory, it would be impossible to decipher the chicken scratch to a degree that it was identifiable.
So why do people insist upon writing illegible signatures?
Are they so arrogant that they feel the need to make their "mark" even more unique than it already would be? Did they never learn cursive writing? Are they abnormally paranoid about someone being able to duplicate their signature? (On the latter point, it seems as though a "large loop and a wavy line" would be easier to copy than an actual legible signature.) Are they trying to disassociate themselves from the document by hoping no one will recognize their name? Or are they just freaking lazy?