Besides engraving which removes material from the section being engraved you can also use welding to write stuff by adding material in the form of a weld bead over the surface (assuming you have skills and tools to do that or know someone who does). I've used that method to name several of my creations. Basically you just write what you want to write with a smooth weld bead on the surface of one of the tubes. Obviously only works with metal frames.