When you open QuickBooks Desktop for the first time, you notice there are two @@ at the end of the title bar, whether it is opened in a single-user or multi-user mode.
Although one instance of QuickBooks is opened, you may have launched the second instance of QuickBooks to run.
Manually close QuickBooks Desktop
Note: Make sure when you double-click the icon, you do so only twice. Clicking more may cause a second instance running and the @ symbols to appear.
If the symbols continue to appear in the title bar, close QuickBooks Desktop and open the Task Manager.
Note: Remember to not exceed two clicks when opening QuickBooks from the icon. You also have the option to open QuickBooks from Start > All Programs > QuickBooks > QuickBooks Enterprise Solutions - Industry Edition 16.0.