1. border! ALWAYS use a border.
2. i would change the placement of the 2 pics of papi. usually one on the left and one on the right would be a good plan.
3. the logo of the red sox should be moved up so you can see it alittle more and not see blue at the top of the logo.
4. while the repetitive "red sox" background will do for now while you're trying to improve the rest of the sig, but in the future, id go another route.
5. spice up the text alittle bit. DL some fonts from dafont.com instead of just using generic text.
my main advice to you right now is just work on placement of the pics, cutting, etc...dont worry about the bg and text too much right now. if you get the player cut out right and placed on the right way, you can then work with blending/lighting/effects on the player THEN worry about backgrounds, THEN worry about text. text is still the hardest part of making a sig for me, and distinguishes a sig from great to just good in my opinion. hope my advice was helpful