From the Terms of Service:
Anything close to spam will be deleted and we might inform your ISP. We log your IP address.
http://www.city-data.com/forumtos.html
For forum regulars:
As many of you are aware, this forum sees quite a bit of spam. Please don't be afraid to use the report post button on the top right of every post if you see a poster spamming, advertising, or trying to solicit members of this website. Even if you are not sure, please report the post anyway.
Thanks all!