Other meta sites have this feature and it seems quite popular.
I think, it would be a wonderful way to promote other german SE sites, for example...
Community Promotion Ads were introduced to give any public SE community a tool to promote things:
The goal is to help visitors find out about the cool stuff your community is doing and help promote activities they find important.
This feature is not available for sites in public beta but is very welcome on all graduate sites.
It is a very good means to promote us on other sites of the network where we are a member but we can not yet publish any such ad on our site.