Sounds like you had a close encounter of the 32nd kind. I'd suggest you report this attack by alien spacecraft to the pentagon but they will probably cover it up and call you a lunatic. The aliens must have a strange ray gun that leaves grease spots on walls. It's a good thing they didn't zap you.
You might try some stuff called "goof off". Also alcohol, mineral spirits, acetone, or thinner. If all fails, then you may need to put on a bin or zinnser undercoat and repaint.