Bear in mind there are two reasons to cover up something.
1. Convenience for printing, or tidying something with no secrecy implications. You can use any number of ways to do this.
2. To remove information that is private, or sensitive, or legally restricted. Almost all the ways of hiding stuff have been used and they all are useless, because the covering can be removed. Only functions called "redaction" are designed for sensitive stuff.
Europe, Middle East and Africa