I've now twice gotten the following notification on Area 51:
Welcome to Stack Exchange Area 51!
user thought you'd be interested in this proposed Q&A site. If you like the idea, you can click the "Commit" button below to be notified when the site is created.
both for a proposal that I was already committed to. How do these notifications work, how can I send them myself? And are they only displayed if you visit that specific proposal?