Coat of arms of Purnell

The blazon

ar. on a fesse sa. betw. three lozenges gu. as many cinquefoils of the first. — Crest, on a wreath, out of a mural coronet ar. ( another or,) a demi griflSn, segreant, erminois, in his' dexter claw a thunderbolt ppr. [Granted to John Purnell, of Stancombe Wickselm, Forward and Dursley, Gloucestershire, 1768.]

A blazon is the description of a coat of arms in the technical language of heraldry. The drawing comes from that text, and from nothing else.