In my Celtic Fervour Series, when my Celts in Britannia have engagements with the Roman Army, the leaf-shaped pugio seems to have been part of the uniform for some of the soldiers and mounted cavalry (Late first century AD). What is not clear is whether the pugio was standard issue to some soldiers only, or whether it was an optional weapon of choice by particular soldiers who gained some kudos from the wearing of it. The lack of sufficient written evidence, backed up by physical evidence makes proving this a difficult task.
The Roman historian Vegetius seems to indicate that the pugio was like the gladius in that the favoured use was for stabbing, though there are depictions of them being used for slashing or cutting.
However, there is much conjecture over the actual use of the pugio. The name pugio may have its origins in the word pugnus meaning fist- the closed fist position of the hand necessary around the hilt to retract it before using the weapon effectively by the left hand. Alternatively, it could also be derived from the stabbing or punching movement a pugilist would make during a fist fight.
Evidence of pugiones and their scabbards seem to indicate the dagger had more than one function. Some of the daggers have very ornate designs etched on them and many of the scabbards found are works of art. The conclusions drawn are that by the late first century AD the pugio held some prestige value as well as being a secondary weapon- the weapon having gone through some changes in shapes during the first century AD. Two different shapes of blade appear to have been used: the leaf-shaped version and a slimmer version with a tapered point was also used.
In my time-travel novel set in the early third century AD it's thought that the pugio had gone through a time of less use druing the second century AD but then had soemthing of a revival. These conclusions are hard to prove, though, since there is scant evidence to show for this.
Whether the wearing of the pugio was earned, or acquired through having sufficient money saved to purchase one is still undecided. Till conclusive evidence appears of the use of them we can make our own conclusions.
This site shows some very ornate scabbards for Roman pugiones.
See some examples on my Roman Research Pinterest Board.
Look out for more coming on Roman weapons sometime soon...