By clicking on the "Settings" gear in Motion Amplification, in the ROI Options section of the window, you can select to "Show ROI Names." You can specify if the name contains a Number, Letter or custom Prefix. You can also change the font type and font size of the ROI Label.
Here are examples of different ROI Names:
An ROI Numbered 1. You will also see the name in the associated plots. (Green boxes added for emphasis.)
An ROI Lettered A. You will also see the name in the associated plots. (Green boxes added for emphasis.)
Tip: You can mix and match Names. By adding some Numbered ROIs then switching to Lettered, you'll get 1, 2, 3 then A, B, C all visible on the screen at the same time. Shown below with a custom prefix.
Tip: You can override the default name by selecting the ROI, the ROI Properties window will appear and the "Name" field is editable.