For quick and dirty brass I just use a spring loaded carbide drag engraver. I bought fancy tips and diamond tips, but one day I needed something done and those were all broken so I just chucked a broken carbide end mill in my lathe and put a grinding wheel on a rotary tool in the tool post and made a conical point. The one in this video has engraved about 60 plates like this one and has not needed to be sharpened.
It is not a "smooth" finish, but it looks good.
[ame=http://www.youtube.com/watch?v=MiVmrCznntE]CNC Engraving a Brass Plate - YouTube[/ame]
I have also used it to engrave my name on the side of impact sockets when I was testing to see what it would do. On hard steel like that it leavesa nice mark, but does feel smooth.
Bob La Londe
http://www.YumaBassMan.com