When you search for a person name in Facebook Search and if you see a grey clock symbol besides the person, then it means that the person name is already searched by you.
For example, in the following image, there is a grey clock symbol appears before the name Mark Zuckerberg, means that this name is already searched by the user in Facebook.
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If you don't want to see the names then , click clear history option in the Facebook Search bar and remove the specific name or all names stored in the history.