In some high-security or “Top Secret” environments, displays (and phones, IoT-devices in general) are often shown with a prominent colored border (e.g. yellow, red, or purple) around the entire screen. This is usually described as a security marking to indicate classification or handling rules.
I am wondering whether the three major desktop operating systems (Windows 10/11, macOS current, and Linux WMs) provide any built-in or even OS-level mechanism to render such a persistent, always-visible screen border.
Specifically:
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Is this functionality implemented at the OS / window-manager / compositor level in any of these systems?
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Or is it typically achieved via user-space software (e.g. a fullscreen overlay, accessibility feature, or custom driver)?
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Are there documented APIs or system features intended for this purpose, rather than ad-hoc tools?
My assumption is, in such environments that this cannot rely on a simple userland application that could be closed or bypassed, so I’m interested in how this is realistically implemented on commodity operating systems.
