I don’t currently see any ad on Italian SE. Is it just me or is this site not yet involved in the new ad policy?
I looked into it a bit, and it seems that the answer is... it's complicated.
Ads are a priori on all sites, but this is not borne out in practice. There is however no official list on which sites have ads and which haven't, and I assume this depends on SE anyway: if they decided to add ads it would probably take just a click.
Furthermore, which ads you see, if any, depends also on your geographical location: if there are no ads available for your country, they simply won't display ads.
All in all it's really hard to figure out why some people get ads and some do not, and there's no real answer to the title question.