sparkles48 posted this over in the Coach forum - might help but (as always) proceed with caution:
"UNOFFICIAL HOW TO REMOVE A PEN MARK TIP!
We've had success with this on SOHO white & pink leather bags so far. Buy a bottle of rubbing alcohol (85 cents a bottle at kroger), dip a cotton swab in it. Gently blot the cotton swab with a paper towel. Rub the swab gently over the pen mark and it should come out!
IMPORTANT - if you're nervous about trying this out, test it on a small patch of leather in an unnoticeable spot first to see that it doesn't damage the leather. This tip is for COACH leather bags only, so use it on other bags at your own risk."
I've dabbed the tiniest amount of perfume on one of my soft leather bags. DO NOT rub through, just hold a cotton wipe against it and it should suck out the ink. The sooner you do it the better as ink which is "old" is more stubborn. As stressed though, if it's stubborn, do not rub as the leather colour will fade. Good luck
There is so much misinformation on the internet particulalry about leather and its care and repair and ink removal seems to attract some very bad (even potentially damaging) sugestions.
Generally speaking most household products have not been tested on leather and should not be used as they can do damage.
For further advice:
Ink is not a straight forward cleaning problem. The ink has redyed the leather so needs careful removal.
If the ink is on a pigmented leather then the first thing you should try is an ink stick (find one that is a professional product used in the industry). The fresher the ink the more chance you have of removing it. If this does not remove the ink then stronger products will need to be used and this is best left to a qualified technician as recolouring may be necessary.
If the ink is on an aniline style leather then the ink has redyed the leather and this would definitely need professional attention from a qualified technican.
Using hairspray/WD40 and all these other solvent cleaners is very risky as it can make the matter far worse as it can spread the ink over a bigger area and can sometimes then be impossible to fix.
Using alcohol, perfume, etc. can also be risky depending on how stable the finish is. If the finish is unstable this would remove pigment form the leather.
Nail varnish remover or any other solvents will also remove the finish and pigment which will need replacing.
DO NOT USE Baby wipes as they are about the worst thing you can use on a leather as they break down the finish and will eventually ruin it.
Please do not try milk or toothpaste these are silly ideas that will leave sticky residues on the surface which will help to break down the finish on your leather.
MAGIC ERASERS should not be used to clean leather in any circumstances (we have just tested these) and they will remove finish and pigment along with the ink. We have just tested these and they really do a lot of damage on leather. They act like a fine sandpaper and remove the finish.
Old ink will be harder to remove than new ink and may mean resorting to solvents which will also remove the finish. This is probably best left to the experts.
Silicones/ polish are the worst thing to use on leather as they will form a coating on the surface of the leather which will not allow any moisture to get to the leather and will eventually break all the finish down and make it crack.
Leather does not need conditioning it needs cleaning and protecting on a regular basis with water based products this will keep it rehydrated and supple. Oils will make things much worse.
Leather should be cleaned gently not scrubbed so 'elbow grease' will only do damage to the finish.
Hide food will not remove ink and will leave residues on the leather which will attract dirt and oils.
Using a good quality leather protector (one that works) will help make this problem easier should it happen again, it also does your leather good by protecting it against oils and dirt which ultimately make the pigment crack and the leather deteriorate.
Whoever suggested that Purell hand sanitizer takes off ink stains on purse interiors is brilliant. Great suggestion!! I just used it on a canvas lining and most of the ink came out - and it was a big stain! Just make sure that you keep rewetting it and blotting with a cloth. Oh yeah, make sure that it has alcohol in the sanitizer.