All Sia release binaries are signed, which allows you to confirm that the version you've downloaded is indeed the exact version that we've released. This is an extra security check to ensure you're using legit, unmodified software, which can be pretty important when the app also handles money like Siacoins.
Download and import the Sia signing key.
wget -c https://sia.tech/releases/sia-signing-key.asc
gpg --import sia-signing-key.asc
Download the signed hash file, and verify the signature.
wget -c https://sia.tech/releases/Sia-v1.5.0-SHA256SUMS.txt.asc
gpg --verify Sia-v1.5.0-SHA256SUMS.txt.asc
If you downloaded a zip file, unzip that first.
Check that the files you downloaded were signed.
sha256sum --check --ignore-missing Sia-v1.5.0-SHA256SUMS.txt.asc
You should see "OK" next to the files you did download and errors for the files you have not downloaded.