New Omega owner.

Hi all
I'm a newbie on here so please go easy on me.
I've just inherited my Great Uncle's old DeVille and I love how a simple watch can look so nice.
Its a day/date DeVille Automatic (non Seamaster) I've had the watch cleaned and it keep time perfectly (in fact it started up and kept great time after being sat in a draw since 1990) and managed to get the serial number to do some research.
The S/N is ST 166.0162 which, according to the Omega database, is a stainless case. This one is gold? The only info I can find online is for stainless steel ones..
There are a couple more markings on the case that I can't find any info on so was hoping someone may be able to clarify what they mean.
They are between the strap lugs on the bottom of the case. The marking are the Omega symbol - 20 - S
Can anyone shed any light on the markings?
Thanks
Steve

would help no end if you posted some pictures....

Here's some pics:

I believe (and may not be right) the markings may suggest the makeup of the case materials: 20 meaning 20 microns of gold plate (on a base metal like brass) for the top, and steel for the lid.
Wait for others to concur or refute!

Nice little watch - the omega db often doesn't call out all materials or dial styles, so I think this one being gold plated is ok (166.0162 is the case ref, not serial no).. Its a cal 10xx - you mentioned having it cleaned, but after 24 years if it wasn't lubricated at the same time stop wearing it until it is, as there won't be any oil left. Slap it on a new strap- I think black or brown gator would work - and it'll look great...