"Not gonna lie; I kind of keep expecting you to post one day that you threw down on someone who clearly had no idea that today was NOT THEIR DAY." ~dontcallmeshirley
Rubbing alcohol or acetone for black ink. If it is blue ink there is no telling because it can be created using tons of different formulations and it never comes out.
I used hand sanitizer with great success only because I couldn't find our bottle of rubbing alcohol so grabbed the first thing I found with lots of rubbing alcohol in it. It was black ink.