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. 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.