From Old English, in particular Scottish, meaning 'weapon show'. Was originally a gathering of troops in every district in Scotland to satisfy military chiefs that men were well trained and their weapons were in good shape. 

Word was adapted from Old Norse.  Wapenshaw is short for the Scottish term 'wapenshawing'.  

A wapenshaw jacket:  

Also described as a motorcycle jacket. 

What is interesting here is that today's word "wapenshaw" links to a previous word of the day, "wapentake". Both use the Old English "wapen" meaning weapon. They also have similar meanings when they refer to a gathering of people from a particular area, with their weapons. Yes "wapenshaw" refers to gatherings in Scotland and "wapentake" refers to gatherings in England. As "wapen" comes from Old Norse "vapn" it is not surprising that it would be used in both Scotland and England.

John Faed (1820-1902) painted "The Wappenshaw: A Shooting Match" and it became his most important work.   It was displayed at the Royal Scottish Academy in 1863 and The Royal Academy in London in 1866. 

Two plus hours on this word and I did it yet again, a stupid gesture and poof, all gone. So this is a very short version(read much) of what I had.

Not much to add on what has been said, but a lot of interesting reading on anything I found. Including this way out find, a Scottish reel?!?! :

ワーペンショウ　、ザ 　 （The Wapenshaw）　：カズのFDDB

One item of note, wapenshaw, was possibly a precursor to the formation of the Scottish territorial army.

Also found in: Dictionary.

Last, but not least. Depending on where and who you ask.

Scrabble does or does not recognize the use of this word, however you choose to spell it. I vote yes, if you are asking.