I received the same response on Saturday. Although it doesn't make sense that he would sign the letter, it is definitely signed by someone, and it does look like his real signature.

Does anyone know if these letters are authentically signed?

Hi Blackhawks026

Thank you for your feedback

Fanmail

What reason did he have for not signing it?

On August 15th, 2011 I sent him a request to an address in the UK (I don't know what the address was). Today, March 23rd, 2013, I got my stuff back unsigned. It was sent back in my SAE, however it was sent from somewhere in NY (even though I had originally sent it over to the UK). He sent back my picture, dvd cover and the UK stamps I had sent. There was also short note explaining why he couldn't sign my item... and the note was signed (not AP or PP) by James. I'm not sure if it was a sec or actually him lol. Either way though, I got another success from him a few months ago from a different address so this fail doesn't really matter to me.