A pen or marker with permanent ink may write on your metal surface without smearing. Brands that feature permanent pens and markers include Sharpie and Marks A Lot. You can find permanent pens in an array of colors at grocery stores, hardware stores and art supply stores.
Pens and markers with paint instead of standard ink may work on your metal surface. Try a latex paint over a water-based one to ensure that it won't smear or wash away if water touches it. You can find latex-paint pens at art supply stores, paint stores and hardware stores.
Some pen brands, such as Nissen, make pens that are designed to write on metal. Often called metal markers, they come in various tip sizes and dispense permanent ink. You can also find markers that can write on hot metal or that come in a bottle instead of a pen barrel. Metal markers are often in stock at hardware stores and art supply stores.