Bill,

It is my understanding that the dirk is only to worn with regimental attire or as outlined by that particular regiment. Every regiment has guidelines as to how to dress, what to wear and when to wear particular attire.

You will see many pipe bands that wear regimental type uniforms which includes the wearing of a dirk. As far as pipe bands are concerned the dirk is only worn with a regimental or military type uniform although you will see bands that will wear them with an Argyle which is actually improper.

But like everything else you will find that people will wear what every they want despite traditions, customs, regulations, and simple good taste. There are plenty of pictures posted on this site which are examples of that.