William was Hereditary Marshal of Ireland; not to be confused with the Marshals of England.
He was killed Bannockburn in 1314.
He appears in The Caerlaverock Poem, K3, where he bears
Gules a bend of five fusils or
The poem gives
la bende de or engreellie portoit en la rouge baniere
but at this time there was no signficant difference between engrailed, indented and the bend as shown