Facebook alerted journalists by mail — snail mail, not email — that it will debut a new product next Thursday (June 20) at its headquarters in Menlo Park, Calif.

Joanna Stern of ABC News reported on the event and scanned the invitation she received, saying that it arrived in a “clean white envelope sent via snail mail.” It read:

A small team has been working on a big idea. Join us for coffee and learn about a new product.

As was the case with previous Facebook product announcements — such as those for Home, the revamped News Feed, and Graph Search — details were scarce.

When Facebook introduced hashtags earlier this week, it summed up the announcement by saying:

Hashtags are just the first step to help people more easily discover what others are saying about a specific topic and participate in public conversations. We’ll continue to roll out more features in the coming weeks and months, including trending hashtags and deeper insights, that help people discover more of the world’s conversations.

Something along those lines is a possibility for what will be announced next Thursday. Or it could be another mobile product, or, really, just about anything.

Readers: What do you think Facebook will reveal at its June 20 event?