I don't THINK it, I KNOW it, because it is NOT an approved app for government communications. Period. And you can't just install apps on government managed devices that handle classified (and even SBU) data. AND there was an NSA Opsec special bulletin warning DoD and intelligence staff about Signal vulnerabilities and that it was NOT TO BE USED for non-public official info
See this: https://www.npr.org/2025/03/25/nx-s1-5339801/pentagon-email-signal-vulnerability
But I'm betting you knew that.