You can read about the court filings [1] for Whatsapp metadata (unencrypted), but the actual text communication from Whatsapp is secure - or at least not returned by subpoena.
I think Signal doesn't even have the metadata available, but I'm not sure about that.
Someone already tried requesting data about two suspects from Whisper Systems. What they got is "one number is not a Signal user, while the second one created his account on X day at Y time."[0]
So yeah, Signal doesn't retain metadata. All they can provide is whether you're using Signal or not and when you've started using it.
I think Signal doesn't even have the metadata available, but I'm not sure about that.
[1] (Horrible Forbes Link)
https://www.forbes.com/sites/thomasbrewster/2017/01/22/whats...