I own an embarrassing amout of glocks really know nothing about sigs an ex friend/shooting buddy had a W Germany P220 that I shot on on several occasions  now im thinking of picking up one of my own.

What do I look for in  used/police trade in 220's? Definitely want one without the rail

The smilies on the muzzle end of barrel are a good indication of how much it's been fired, lack of any black on the barrel end means it's been fired a lot, that isn't a deal breaker.

Remove the slide and take a look at the anodizing along the rails, it should still be in good shape, no chipping or damage.

If the rails on the receiver are wavy, referred to as mud rails or scalloped rails walk away without leaving a forwarding address or name.

I have a few W.German Sigs and they are my favorites. 

OP - read this:
https://grayguns.com/guide-to-sig-sauer-pistol-inspection/

There is a guide at the top of the SIG page too:

http://www.ar15.com/forums/t_5_14/86894_Guide-To-Sig-Sauer-Pistol-Inspection.html

The Sig 220 is my second favorite .45, after the 1911.  Really nice to shoot.  And, it's a Sig.

You can always buy a SIG 1911.....it's like crossing the streams

I read the inspection blog/post a long time ago (was going to say 10+ years, but see it was written in 2009.  So at least 5-6 years ago).  My rails were silver and I though "Oh no!  I'm screwed".  That was around the time I started shooting considerably more (1996 p229 bought new in 1996) and there has been no change in the rails.  Granted, a lot of shooting for me would be 1-2000 rds/year (and lots of folks shoot that in a month)

I did switch to grease from oil after reading that, not sure if made a difference.
I can't imagine that anodizing will remain on the rails with extended round counts, I'd love to see pics of guns with a few thousand rounds and shiny black anodizing.

Sooo, I personally wouldn't worry much about the rails.  All the other points are really good.  Of course, if you DID find a used SIG with perfectly black rails I would take that as a very good sign.

here are a few pics of my frame rails... sorry but I don't have a very good camera...my rails are mostly shiny black with just a few slight light spots showing toward the rear...I just shot yesterday and most of what you see is grease and debris...I'll try and post a pic later after I clean it.  Unknown round count but I included pics of the barrel maybe someone could chime in...

OK I went outside for better lighting... my frame rails show just a bit of wear on the rear... the rest mostly dull or shiny black... it was well greased when I got it, and like I said maybe the barrel wear posted above will give some indication of round count.

I believe it is the undersurface of the rails that matters.  Take a picture looking up from the grip/magwell side.  Once again, I don't put a whole lot of value in the color of the rails.  IF the undersurface is still nice, black anodizing that would be a good sign, but don't run away if they are silver.

Thanks everyone a 220 wil be next on my buy list

A German 220 is headed my way should be in my hands by the end of the week

Good luck with your P220

Picked this one up for $399 at a pawn shop. It was a police trade in that was worn a lot, shot little.

Sounds/looks just like the one I picked up today definitely looks well cared for nice and clean well lubed. Gave $405 on GB +17sh+25 transfer so a short 450 in it