Leather World Technologies offers a full line of professional grade ink, stain, and degreaser products for restoring your leather to top condition. Once your stain problem has been resolved, we have the leather care and leather cleaning products to maintain your leather for years to come.. . The leather manual contains a stain problem solving section at Problem Solving Tips that lists a number of common leather staining problems and the corrective action to take, including the appropriate products to use. . . In general, you'll find that most of our care and stain remover products can handle Pigmented and aniline leathers. Special products are provided for NuBuck/Suede leathers. If you aren't sure of your leather type, consult Identifying Leather..
http://www.leatherworldtech.com/category.aspx?categoryID=50. . I've used acetone to remove pen marks on leather before. It is a deglazer though, and needed oiling after. I hope it's not white leather.. . or take a can of cheap hair spray, the pressurized kind. spray some on a dry towel, from close enough range to make a "wet spot" on the towel (3-4"away). . use the BACK side of that spot on the towel to rub the ink. . PRESTO, it's gone!!!