How to sign out in icloud on all your devices is to open a browser and log in to your Apple ID account page. Navigate to the Devices section and pick each device shown. Press Remove from account to unlink them. Besides that, you can reset your Apple ID password, and that will compel all devices to log out, signing out automatically. Then, you must manually log out on any devices left by accessing Settings (iPhone/iPad) or System Settings (Mac) and selecting Sign Out. In this way, your iCloud data will no longer be accessible on the devices connected to Apple Inc. services.