Etching steel? Yes

It appears to be totally dependent on the steel. As originally advertised the glowforge was supposed to do absolutely nothing to steel unless you used a material like Cermark. Since its release people have found some steels to take a mark with nothing but the laser, for some steels a thin layer of mustard seems to leave a mark. Dry Moly works on many and of course Cermark should work on pretty much anything the instructions say it will work on.

You can search on Cermark settings and be pretty confident it will work. For all others you may need a sacrificial knife to dial in your settings and process. Some threads on these techniques: