Shaking hands. A relic of the ancient custom of adversaries, in treating of a truce, taking hold of the weapon-hand to ensure against treachery.
Lady's curtsey. A relic of the ancient custom of women going on the knee to men of rank and power, originally to beg mercy, afterwards to acknowledge superiority.
Taking off the hat. A relic of the ancient custom of taking off the helmet when no danger is nigh. A man takes off his hat to show that he dares stand unarmed in your presence.
Discharging guns as a salute. To show that no fear exists, and therefore no guns will be required. This is like “burying the hatchet” (q.v.).
Presenting arms - i.e. offering to give them up, from the full persuasion of the peaceful and friendly disposition of the person so honoured.
Lowering swords. To express a willingness to put yourself unarmed in the power of the person saluted, from a full persuasion of his friendly feeling.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894