How does it indicate it's on?

Open System Preferences> Spotlight> Privacy.

Drag the folder or Disk you want indexed into the Privacy panel.

This switches indexing off for that item.

Highlight the item and then click the minus button to remove it from the panel.

This should force Spotlight to index it.

To check click on the Spotlight icon in the menubar, enter a word

if Spotlight is indexing you should see a indexing progress bar.

In Big Sur, once one has initiated Spotlight indexing, you need to click on the Spotlight icon in the menu bar and enter a search term to see the prominent indexing progress bar…