Here's how you can turn on the fast user switching option in OS X on your Mac.
1. Go to System Preferences.
2. Go to Users and Groups.
3. Click the lock icon, and enter your admin password.
4. Go to Login Options.
5. Click the "Show fast users switching menu as" checkbox.
For more, see the original article at the link below.
5 Essential Time-Saving Tips for OS X Mountain Lion | TechnoDuet