From Open Whisper Systems:

In the “first half of 2016” (the most specific we’re permitted to be), we received a subpoena from the Eastern District of Virginia. The subpoena required us to provide information about two Signal users for a federal grand jury investigation.

This is the first subpoena that we’ve received. It originally included a broad gag order that would have prevented us from publishing this notice, but the ACLU represented us in quickly and successfully securing our ability to publish the transcripts below. We’re committed to treating any future requests the same way: working with effective and talented organizations like the ACLU, andpublishing transcripts of our responses to government requests here.