I saw this on a white board today. Usually it's a debate-related or argument-related term. If you don't speak up, the default assumption is you must concur. Ah, there's even a Wikipedia article related to my understanding of the term from high school speech. But the context in which I saw it today clearly made it a security-related statement. E.g. if you don't talk, someone can't go phishing on you, listening for names and details. So despite the rather 1984 Orwellian nature of the statement, I understand where they're coming from given the number of contractors and sales folks who try to get me to talk in order to find additional names and details they can use to show they know something and know someone, so it must be safe to tell them more.
Snarky: I'm sorry you don't like the new security program. But look at it glass half-full. It's only a proof of concept.
Title: I don't think this is what's meant by Silence is Compliance.