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I've found out that there is no "Sign Out" link on the Site. Looked at bottom and top and all over the page. Nor it is present in the user page.
Where is it? It would be useful if present besides the "username" on the top of the page.
There is a Down Pointing Triangle ▼ icon ( blue circle in image ) before the user name, click on it, and you can see the "logout" link.
See the following image,
Clicking Log Out will clear our cookies and log you out on all devices.
You can see the logout link, when you move the mouse over the username.
If you press on the small triangle next to your username you get a new window. On the top of that window there are 3 links: activity, privileges and log out.
If you put your mouse over your user name then a window appears with log out on the right hand side.