Mr. and Mrs. Smith
Mr. and Mrs. Smith is an arbitrary name when used by an (unmarried) couple to check in at a hotel. The name is not taken from a particular Mr. and Mrs. Smith, but is chosen for being the commonest surname in the English language as a transparent disguise.
See also John Doe.
Room, A. (1981), ‘How to Make a Name?’, Naming Names, p.39