Earlier quoted context omitted.
You are speaking of metadata as if all metadata is equal. Signal does collect phone numbers (even though, since usernames have been introduced [1], this can be made opt in from now on), but not the contacts or social graph, neither many other relevant metadata [2]. What they can gather from this, is only when the specified phone number registered to signal services and its last connection to the server [3]. So, if yo…
>but not the contacts or social graph, neither many other relevant metadata [2]. Assuming you trust them (notice all your links point to signal.org own publications). Most of the privacy people are cautious/paranoid and assume that everything that can be collected is collected. Even assuming a lack of malicious intent, what's stopping NSA from hacking into Signal's infrastructure and logging who's talking to who alon…
Sealed Sender, the second link in the comment you've replied to. The indicator is off by default, but you can enable it under Settings → Privacy → Advanced. If I remember correctly, it doesn't work for the very first message you exchange with someone, but then it turns on and remains on.
In layman terms, it turns "from A; to B; content: " into "to B; content: ". Their infrastructure doesn't need to know the "from" part to serve its purpose, so they strip it away.
If it was the other way around, they'd have to give that info to the (US) court. Same as any other US-based business, it's not optional, they can't ignore such requests, they can't lie, otherwise they'd be placing themselves in legal troubles for a random nobody that happens to be using their product. So, when I see this page, I fully believe them: https://signal.org/bigbrother/. If I didn't, my first step would be to look up those court cases from alternate sources.