Everything is very off. I have seen a handwritten Jeter letter and it looks nothing like this. This appears to have been written by a female. Also when just signing "Derek" he does not write it out he signs it with some of his normal signature missing but the D and 1 loop will be present.  

http://www.ebay.com/itm/321189635049?ssPageName=STRK:MESINDXX:IT&am...

Here is how jeter signs his first name and notice the lettering of sanderson looks nothing like the hat above.

http://www.ebay.com/itm/Derek-Sanderson-Jeter-The-Dive-autographed-...