I don't know for sure, but you might be able to use a little dab of essential oil to remove it. Like acetone, essential oils are solvents, although most essential oils are much less harsh than acetone, and even if it doesn't work to remove the marker, it won't damage the leather. I don't know if all essential oils are solvents, but I know that citrus ones are, as well as winter mint essential oil. I'm sure many others are as well, if not all of them. I do printmaking and those are just a few I have used. They're often available in the skin care area of stores like Whole Foods, or at craft stores for scenting soaps and things. If you have something like Goo Gone, essential oils are why it works, though some other chemicals are added.