Thomson Clan Crest:
Why we have this crest for the name Thomson
The first evidence of a crest we can find for the name Thomson is from the arms of Alexander Thomson, Bute Pursuivant (and therefore a Herald) registered arms on 01/07/1724, and for his crest had: A thistle proper, motto Pro patria.
As well as the crest from the arms of Alexander Thomson On the same page of the Register is John Thomson of Charlton (crest: A stag’s head erased proper, motto: Honestie is the best policie).
And also on the same page, Andrew Thomson, Advocate in Aberdeen (crest: A crane holding in its beak a twig of palm proper,motto: Curae cedit fatum – Fate yields to carefulness). Any of these could be used as the crest for the name Thomson. We have chosen to take the first from the Herald Alexander Thomson as it was the earliest and held more weight as he was a Herald.
The Thom(p)son Society Crest
The Thom(p)son Society have registered a crest for the Society. This can be worn by members of the Society but is not the crest of the Clan (as in can be worn by anyone of the name Thom(p)son).
This is a corporate crest of The Clan Thompson Society: Crest a Border Reiver on horseback Proper, and in an Escrol over the same this Motto ‘DENY US NOT’
Thomson Coats of Arms
Arms of Thomson of that Ilk
The “elder” coat of arms was recorded in Sir David Ogilvy’s Seton Armorial (1591) as:
Thomosone – Argent, a stag’s head cabossed Sable charged between the attires by a mullet Gules. This is not in the Register of All Arms.
Argent, a stag’s head cabossed Gules attired Or and on a chief Azure a cross crosslet fitchy Or between two spur-rowells Argent Cannot find any crest part of this.
The arms of 18 Thomsons from Gayre’s Roll of Scottish Arms plus the shadowy Thomson of that Ilk and Allan Thomson
Remaining Thomson arms in the Lyon Office Ordinary, vol.II. The first coat of Roy Herbert Thomson have been omitted since, on becoming Lord Thomson of Fleet, he changed the original moose-head in his arms to the usual Thomson stag’s head. The moose was appropriate for a Canadian, but perhaps he became a British subject and felt it necessary or desirable to Scottify his arms.
Theodore Radford Forrester Thomson (1897-1981)
Potent Argent and Azure on a bend Sable a mullet between two stags’ heads cabossed Or
A gauntleted hand erect in pale holding a flaming torch in bend proper
Above the Crest: Acquanimitas (With Even Mind)
Below the Shield: Veritas Praevalebit (Truth Will Prevail)
William Thomson (1824-1907) Lord Kelvin, Baron of Largs
Baron Kelvin of Netherhall, Largs
(knighted Nov. 10th 1866, raised to the peerage in 1892)
Lord Kelvin Lord Kelvin
Argent, a stag’s head cabossed Gules, on a chief Azure a thunderbolt
Proper winged Or, between two spur revels of the field. 
Crest: A cubit arm erect vested Azure, cuffed Argent,
the hand grasping five ears of rye Proper.
Supporters: Dexter: A student of the University of Glasgow, habited [Gules],
holding in the dexter hand a marine voltmeter.
Sinister: A sailor habited [Azure], holding in the dexter hand a coil, the rope passing
through the sinister, and suspended therefrom a sinker of a sounding machine, all Proper.
Motto (over the crest): Honesty without fear.