Throughout my early life, whenever my grandma would get me a gift, she would write my name on it. Bought me a teddy bear? A mug? A baseball bat? Optimus Prime? All of it marked permanently with my name on it. It frustrated me as a kid as much as it does now, because it's not the kind of thing anyone would ever want. I couldn't even donate it or sell it at a garage sale when I didn't want it anymore, it just became trash.
I figure that Null's signature would be the same thing.