Whats wrong with my phone... the screen seems ot have a transparent "inkprint"?

i have a windows phone 7. a samsung focus. ive been noticing for a while there seems to be a really faint inkprint etched into the underside of the LCD screen for some reason, i can see the little symbols and all the keypad (at times, depends what screen im on, light or dark i mean) , YES ive dropped the phone, but NO its not damaged badly (i hope) im a real klutz, if anyone thinks they know whats going on with my baby, please T.T please im begging you. help me.