Romans 16:16 -- Salute one another with an holy kiss. The churches of Christ salute you.
It was a kiss; a form of greeting (salute).
It was holy and chaste; not lascivious as the woman in harlot's attire (Prov. 7:13ff. So she caught him, and kissed him, and with an impudent face said unto him...).
It was sincere and open; not false and treacherous as Judas (Luke 22:48 Judas, betrayest thou the Son of man with a kiss?).
It was mutual; salute one another (Rom. 12:5 So we, being many, are one body in Christ, and every one members one of another).
Unlike the Dead Sea, which is constantly receiving but never giving, a mutual expression flows in both directions. This mutual expression was one of love -- By this shall all men know that ye are my disciples, if ye have love one to another. Of respect -- Be kindly affectioned one to another with brotherly love; in honour preferring one another. Of familial bonds -- Let there be no strife, I pray thee, between me and thee...for we be brethren. And I myself also am persuaded of you, my brethren, that ye also are full of goodness, filled with all knowledge, able also to admonish one another.
John 15:12 -- This is my commandment, That ye love one another, as I have loved you.