Show corresponding icons for each monitor on task bar

In the settings app under the taskbar options, set the option Show Taskbar button under Personalization->Taskbar to "taskbar where window is open"

On Windows 7 I have personally tried two options:

DisplayFusion

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/