Displaying Customer Number in ISA

I´m modifying some jsp for ISA. Now, I want to display a Customer Number next to his or her name.

I thought of using the User Business Object for this. I don´t know if this is the correct Object.

I thought I could use User.getUserID(), but that isn´t the Customer Number. Which function do I have to use? If I use the wrong Object, which Business Object do I need to use?