Coat of arms of Percival

The blazon

ar. on a chief, indented, gu. three crosses, formee, of the field. — Crest, a thistle ppr. [Borne by Spencer Perceval, Esq. of Weston-House, Surrey, 1825.]

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.