[jblwps]

As greysonp points out, yes; Signal has had reproducible builds since March 2016. So we can prove that those published binaries do not have backdoors insofar as we can prove that the corresponding source code does not have backdoors.

[mechnesium]

If you didn’t create the binary yourself how can you trust it?

[jblwps]

Because you can reproduce that binary bit-for-bit to confirm its corresponding source code. That's the point of a reproducible build.

https://en.wikipedia.org/wiki/Reproducible_builds