Many times, I have used "Hide comment" when a friend puts an inappropriate comment on one of my posts. Ideally, I and the person commenting are the only people who can see that comment. If the person whose comment is hidden can see that it is hidden, I may lose that friend or worse. Does the person whose comment is hidden see that it is hidden? Ideally, he should not know that it is hidden.
It looks person does not see his comment is hidden.
I did a test with friend and here is the result. He hid my comment:
I did not receive any indication (no notification) that comment is hidden and see no indication on comment: