If you mean on the body of the lens itself, you can use anything as long as whatever you're using doesn't get inside the body itself. If using water, make sure you dry it throughly before storing it away to prevent fungus growth.
I would be extremely careful with using alcohols. Some of the paints might get washed off. Do not let any of the alcohol land on the lens coatings. While I should expect the coating to withstand alcohol, I cannot be sure.