Show corresponding icons for each monitor on task bar
In the settings app under the taskbar options, set the option
Show Taskbar button under
Taskbar to "taskbar where window is open"
On Windows 7 I have personally tried two options:
DisplayFusion is a paid program, but it's a must for Windows 7 + Multiple monitors. https://www.displayfusion.com/
Dual Monitor Taskbar
Dual Monitor Taskbar is a freeware program that works very well for that job, too. https://sourceforge.net/projects/dualmonitortb/