This coin is part of a long held military tradition dating back to the Roman Empire.
A challenge coin is a small coin or medallion, bearing an organization’s insignia or emblem and carried by the organization’s members. Traditionally, they might be given to prove membership when challenged and to enhance morale. They are also collected by service members and law enforcement personnel. Historically, challenge coins were presented by unit commanders in recognition of special achievement by a member of the unit. They could also be exchanged in recognition of visits to an organization.
The Roman Empire rewarded soldiers by presenting them with coins to recognize their achievements. In Rome, if soldiers excelled in battle one day, they would receive their typical day’s wages along with a separate bonus coin each. According to some accounts, these bonus coins were specially minted, featuring the marks of the legions from which they came. As a result, some soldiers apparently kept their coins as mementos, instead of spending them on wine and women. Source
I do not have a date of the coin or the identity for Bill Babb. It is a relatively modern coin containing “Vietnam” on the obverse side of the coin. It isn’t particularly new either as current day versions contain enameled surfaces as part of the coin. So, my best guess is that it is likely from 1970-2000.
This particular challenge coin is currently available via eBay. A link to the item is provided below.