Victorinox introduced the 'Plus-Scales' in 1985 with the new SwissChamp. These scales have a slots for toothpick, tweezers, and a ballpoint pen; sometime later a small hole was added for a Straight-Pin. The pin can be very useful for removing slivers (splinters), or activating small electronic switches typically used for resetting, or setting electronic devices. The Straight-Pin is made from stainless steel.
After the pin-storage-hole was known on the Plus-Scales, the storage slot started to appear on standard Cellidor scales. All standard scales now contain a hole to carry the Straight-Pin even if the actual pin is not supplied with the knife when purchased new.
A Straight-Pin is also featured in all of the current (2017) SwissCard models.
Information from Victorinox dated 2010.02.08 indicates that the straight-pin was first introduced in 1991. We also believe the Plus-Scales became more generally available in 1993.