Coins, these days they call them Challenge Coins, in my opinion this is not the correct wording from historical point of view. I can sum up all the history what is mentioned on Google, but what is the real story ? In what year would be the first COIN made and handed over ? What specific reason soldiers received coins ? Does someone have an official document where the coin is handed over to someone ? Are there specific Citations to hand over the coins ? So what is the historical and most probably correct story why they hand over coins ? Again i know the procedure now, handshake thanks to the receiver, sometimes from the heart, sometimes just because of... I'm looking for the historical background of a COIN.
The earliest example of such a somewhat juvenile secret society practice dates back to around the 2nd Century AD. Tokenised silver coins have been found in Verulamium (today St Albans). They are assumed to have been used by worshippers of Mithras, at that time a forbidden Roman military cult, as a means of identification/admission to ceremonies. More modern varieties may arise from the Short Snorters based on tokenised bank notes first used by Alaskan bushpilots in the 20s but described in detail in the European and Med Theatres by John Steinbeck (see Once there was a War) and now used by some Star Trek Spock idiots - devotees. Probably easier than having to remember some silly handshake!
