The non-existent Clan Gunn crest badge and shield / coat of arms
As no Clan Gunn Chief has ever been recognised by Lord Lyon there is no official coat of arms from which a Clan crest badge and motto can be drawn. That's the straight legal position. I have discussed this idea here http://clangunn.weebly.com/the-non-existent-clan-gunn-crest-badge-and-motto.html
The George Gunn Munro (Braemore) shield of arms is wrongly used by many - see http://www.thetreemaker.com/family-coat-g/gunn/scotland.html
and for which I have been informed that 'a quartered coat of arms was matriculated in name of George Gun Munro of Braemore on 18 November 1800 wherein he is recorded as 'the heir and Representative of the late Sir George Munro of Poyntzfield his Uncle'. ... the shield of arms shown on the website you mention is a reasonably accurate representation of the Arms for Gun that appear '
Now look at Thomas Sinclair's The Gunns (being the seminal Clan Gunn history book published in 1890) front cover and title page, and note the similarity with the image in the above link -
So, the hand and sword at the top, the image on the shield and the stars which many now wrongly associate with Clan Gunn heraldry are merely from the the arms of one Clan Gunn family and have nothing to do with the overall Clan Gunn - and certainly have nothing to do with any Clan Gunn Chief arms.
Thomas Sinclair's book would have popularised (and may even have started) the erroneous belief about the Clan Gunn shield / coat of arms / crest badge. I note he uses 'Aut Pax Aut Bellum' as the motto. Again this motto has no legal validity but I am not aware of any link - one way or another - with the Gunn Braemore coat of arms...