The Naesmyth Crest

The "Crest" is the portion of the "Blazon of Arms" (or Coat of Arms) which sets on the top or at the crest.  Hence, "Crest".

Naesmyth (Nasmyth) Crest

Naesmyth Crest Badge

"Burkes General Armory" decsrcribes the Nasmyth (Naesmyth) "Arms" as:

"gu. a dexter hand couped ppr. holding a sword paleways ar. betw. two broken hammers or."

Translated, this means: the shield's background color is red (gu. = guiles = red) with three devices upon this shield.  The devices are: a right (dexter = right) hand, severed from the arm with a clean line (couped) in natural flesh color (ppr. = proper = natural) holding a silver (ar. = Argent = silver) sword with the flat side showing (paleways), between (betw.) two broken gold (or. = Or = gold) hammers.

Burke further described the Nasmyth (Naesmyth) Crest as:

"A hand holding a hammer, as in the arms."

Therefore, the crest would be:  A flesh colored right hand, severed from the arm with a clean line, holding a broken gold hammer.
To the above-left is Crest 13 from Plate 221, contained within Volume Two of "Fairbairn's Book of Crests of the Families of Great Britain and Ireland" by James Fairbairn, which depicts the Naesmyth Crest.  Fairbairn's text describes this as the crest for;  Down, Downs, Garstin, Hamerton, Naesmith, Naesmyth, and Nasmyth.  Immediately to the left is the Naesmyth Crest Badge with Naesmyth Moto.