I'm also worried about that these days. They posted an article a while back that Signal costs $50m per year to run, and that they make that money from "things". Together with how low a profile they keep, I'm not convinced they aren't a honeypot.
I love Signal and it's still my preferred messenger, but if it came out that they're backed by some government agency, I wouldn't be extremely surprised.
I and not necessarily many, but at least some people I know donate (and, somewhat irregularly, will continue to do so) small-ish amounts to the foundation. [1]
You’d imagine that ought to be sufficient to cover running costs. However, it might actually not be enough with hardware prices these days? Not sure.
They’ve also recently (edit: “recently-ish”, it’s actually been a year!) introduced paid storage for backups, which I’d imagine comes with some amount of profit margin, too. [2]
50 million a year is about 50 cents per user as they are said to have 100M active users. So it's not that bad really. Nothing that would require a 10$/month subscription.
I love Signal and it's still my preferred messenger, but if it came out that they're backed by some government agency, I wouldn't be extremely surprised.