Shaking Hands

What is the origin of the custom of *shaking hands* in token of friendship? And were the *clasped hands* (now the common symbol of Benefit Clubs) ever used as a signet, prior to their adoption as such by the early Christians in their wedding rings; or, did these rings bear any other motto, or posy, than "Fides annulus castus" (i. e. *simplex et sine gemmâ*)?