I was wondering the same thing awhile ago and actually looked it up. If I remember correctly I think it's a financial company. However, I could be wrong.
One of their ATMs outside the ArenA ate my card. Right after I bought an Ajax jersey from the stadium shop. Bastards.
I believe it's ranked as the tenth largest bank in the world. A couple banks merged. Another different couple of banks merged. I think another bank merged with one of the two that had already merged. And then the two different sets merged together forming ABN-AMRO. I have a timeline I got off their website somewhere in my history notes...