Actually I contacted S&W but they said they couldn't do it to a gun that they didn't manufacture. I didn't think of asking SIG.
I did however speak with the the guys at State Line Gun Shop and Paul & Don put me in touch with a guy by the name of Phil Cote. Phil is a sculptor and engraver and said he could do it. He normally uses a chiesel and hammer for blued steel, but because I have a Stainless Steel Slide, he said he can't use a chiesel because the steel is too "Sticky". Suggested "Bedini?? or Bellini? type of stye. I can't remember exactly. He also said he had a carbide tip engraver which could penetrate the steel. Don at SLGS had complete faith in him, because he has seen his work and has had Phil do some guns for him as well. We'll see how it comes out.