Historical coat of arms of Gibraltar, 1836-20th CenturyParty fesswise through the nombril point Argent and Gules, in chief a castle triple towered of the last, pendent therefrom by a chain a key wards downwards in base Or.  Beneath the shield upon a scroll the Motto 'Montis Insignia Calpe' 1836 Description of the coat of arms of Gibraltar, College of Arms
National symbols. HM Government of Gibraltar website
Ian Sumner, British Colours &amp; Standards 1747-1881 (2): Infantry, p. 9. Osprey Publishing, 2001. ISBN 1-84176-201-6
Klimeš, Roman Gibraltar (2011): The Rock with its own Symbols. Proceedings of the 24th International Congress of Vexillology 2011. PP. 675-685
Discover Pocket Guide to Gibraltar. p. 69-70.
Badges, Flags of Gibraltar, Gibraltarinformation.com 
Castle design reference (Commonly version with Incorrect tinctures according to heraldic description)