Seal of Alexander I of Scotland, 12th Century

p103, History of Scottish seals from the eleventh to the seventeenth century by Walter de Gray Birch, 1905

Annexed (at right) is a seal of Alexander I in which he is represented fully cased in the armour of that period.

      Here we find the scaled mail-coat composed of mascles, or lozenged pieces of steel, sewed upon a tunic of leather, and reaching only to the mid thigh. The hood is of one piece with the tunic, and covers the head, which is protected with a conical steel cap, and a nasal; the sleeves are loose, so as to show the linen tunic worn next the skin, and again appearing in graceful folds above the knee; the lower leg and foot are protected by a short boot, armed with a spur. The king holds in his right hand a spear, to which a pennoncelle, or small flag, is attached, exactly similar to that worn by Henry the First; the saddle is peaked before and behind; and the horse on which he rides is ornamented by a rich fringe round the chest, but altogether unarmed. (Seal in the Diplomata Scotice, plate 7. Tytlerís History of Scotland vol. ii. p. 360.)
Source: Electric Scotland

It was portrayed as below in:
The Pictorial History of Scotland from the Roman Invasion to the close of the Jacobite Rebellion. A.D. 79-1646, 2 vols, vol. i, (London, 1859), facing page 64.

Steel engraving and enhancement of the Great Seal of Alexander I, King of Alba (Scotland).

Referenced on p95, Arms and Armour of the Crusading Era, 1050-1350, Western Europe and the Crusader States by David Nicolle
234 Seal of King Alexander I, Scotland, 1107-24
(British Library, Dept. of Seals, London, England)

Here the King of Scotland is equipped in the same style as his English neighbours except that his armour looks slightly old-fashioned. Alexander has a large kite-shaped shield, and a conical helmet of apparent segmented construction with a forward-angled crown and a nasal. His mail hauberk has long, rather broad sleeves without mittens. Judging by the line of an apparent shoe around his ankle but well above his spurs he also lacks mail chausses for his legs.

A Scottish Knight, 12th Century, in Armies of Feudal Europe 1066-1300 by Ian Heath, based on the Seal of Alexander I of Scotland
Other Illustrations of Scottish Costume & Soldiers