Instead of monetizing surveillance, we’re supported by donations, including a generous initial loan from Brian Acton. Our goal is to move as close as possible to becoming fully supported by small donors, relying on a large number of modest contributions from people who care about Signal. We believe this is the safest form of funding in terms of sustainability: ensuring that we remain accountable to the people who use Signal, avoiding any single point of funding failure, and rejecting the widespread practice of monetizing surveillance.
The foundation was started with an initial $50 million loan from Acton, who had left WhatsApp's parent company, Facebook, in September 2017.
The Freedom of the Press Foundation had previously served as the Signal project's fiscal sponsor and continued to accept donations on behalf of the project while the foundation's non-profit status was pending.
By the end of 2018, the loan had increased to $105,000,400, which is due to be repaid on February 28, 2068. The loan is unsecured and at 0% interest.
Privacy is Priceless, but Signal is Expensive
Funding details via Wikipedia