After indexing my LR catalog for face/people detection, I discovered a lot of "faces" that I was not interested in. It's useful to know that these faces are actually subareas of your image that look like faces and are called face regions, even if they're not really faces. Here's how you can ignore or delete those unwanted face regions.
First, recognize that when you open up the People view (Library>View>People or press letter O ), you'll see two different sections. At the top is the Named People section, which has organized faces by the names of people that you have already named. Below that is the Unnamed People section, with faces yet to be named.
Let me walk you down the Named People path first, because although it would seem obvious, you can't delete/ignore faces going this way. So, click on a named person's image in the Named People section and you'll see two new sections. At the top is the Confirmed section, which includes faces from images you'll already confirmed match the person's name. Below, you'll see the Similar section, which includes faces for people who seem similar to faces you've already named. LR provides a suggested name for each face, with a question mark waiting for your choice. Moving your cursor over individual faces, you'll see a check mark showing up in the lower left corner. Click on this to confirm that the suggested name is correct, if it is. You can also select multiple images using the Shift or Ctrl key with mouse click, and then click on the check mark to confirm all of them. However, expect to see a lot of faces with either wrong name suggestions or faces that you are not interested in. I wanted to ignore or delete these faces from this name suggestion process in the future, so that I don't have to see them again. Unfortunately (and oddly), there is no way here to click an X to delete the face region, though it would make logical sense.
The only way I could figure it out was to go down the Unnamed People path at the higher level of hierarchy. Return to this level by clicking on the <People link at the upper left. In the Unnamed People section (below the Named People section), you'll see a set of faces with suggested names followed by the question mark. Moving your cursor over individual faces, you'll see more choices than you did on the Named People path described above. On the left is the same check mark allowing you to confirm the suggested name. On the right, you may see either a circle with diagonal line or an X. The circle choice allows you to chose "no, this is not [name suggested]". That's not the same as actually deleting the face region. Click on the circle a second time, and the X will display. This X gives you the choice to "delete face region". And, as described above, it works to use the Shift or Ctrl key with mouse click to process multiple faces this way.
Anyway, that's what I learned by trial and error. I hope it works for you. And it would be great if LR developers would add the X choice in the Named People>Similar section.
Thank you for the helpful information.