Yes, you can return the screen to the login screen. You''ll need to enable "Fast User Switching" under the Accounts Preferences Pane (Login Options), check the box to to show it as an Icon in the task bar.
Then you simply click it and select "Login Screen" and it returns there without logging you out. When you enter your username/password it returns you to your desktop. It's basically a lock screen but it's what you are looking for.
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