Using a lock icon is helpful for people who want a visual reminder to lock their computer screen. Here are instructions for adding a lock icon to your taskbar ...
To lock or unlock the Windows taskbar, right-click any blank space on the taskbar and select Lock the taskbar. You'll see a check mark if the taskbar is locked.
Lock the taskbar to its current position. Click on the tab labeled Taskbar, then place a checkmark next to Lock the taskbar within the Taskbar Appearance ...