Pocket Knife with Kilt

[MacKenzie]

The bog oak, jet black in appearance, was a very hard wood suitable for the purpose. The handles on the stag knives simulate horn which was also traditionally used. Any ornamentation is merely a reflection of the Highlander's lack of confidence in paper money which resulted in him embellishing much of his personal wearing apparel with silver and cairngorm stones which are of value. Thus he carried on his person most of his worldly wealth. The black dagger (sgian-dubh) was usually carried in a place of concealment very often under his armpit (or oxter). This gives support to the view that 'black' does not refer only to the colour of the handle but implies 'covert' – as in (as stated previously) blackmail or black market. When the Highlander visited a house on his travels having deposited all his other weapons at the front door he did not divest himself of his concealed dagger, since in these far off days it was unsafe to be ever totally unarmed, not because he feared his host but rather because he feared intrusions from outside. Accordingly, although retaining the dagger; out of courtesy to his host he removed it from its place of concealment and put it somewhere where his host could see it, invariably in his stocking on the side of his hand (right- or left-handed).

https://en.wikipedia.org/wiki/Sgian-dubh