I'll take "Lies that your parents told you about how the world works" for 500, Alex.
Serious question though, I thought the whole signature thing was more of a legally binding thing for the signer asserting themselves as X, sort of like checking the "I'm over 18" box. Sort of a "Well we asked you the question, it's not our fault if you lied" type thing.
i went to Germany as an exchange student, scribbled out my random scribble for my travellers check, and they denied me because my signature wasn't close enough to their record. heard a similar story from a friend who visited Japan
Handed the clerk my card during payment, she looked at it and said it is not signed so she is not allowed to accept it. I took it back, she gave me a pen, I signed it and gave it back to her.
She ran the transaction, got an approved slip, gave me the slip to sign, I signed it and gave it back.
She compared the signature on the slip to the signature on the back of the car, and Lo And Behold, They Matched!
There's a big difference between "This thumbprint in blood was on the recovered murder weapon and it's a perfect match" and "This smudge of half a finger on a paper bag found near the scene was arguably a match" but the jury isn't necessarily told about this and where on that scale the evidence they've been told about would lie.