Most references I see to the Trussell Coat of Arms read as follows: Argent fretty, gules on each joint a bezant, a bordure azure ... This is the specification that, for example appears in Burke's General Armory. The description roughly translates, "Silver, trellised red, at each joint a gold coin; all within a blue border". The Goat Crest in this particular version may have been associated with the Trussell's at Billesley since they supported themselves by raising goats in the period following the devastation of the Plague.
It is interesting to note how coats of arms evolved. During the Middle Ages one of the main strategies in war was to wear armor that was increasingly heavy and covered an increasingly larger part of the body. Such a metal suit of armor normally included a helmet, a helmet that made it virtually impossible to identify the individual inside ... but identifying each other was pretty important if you didn't want to kill "friendlies". First the knights painted designs on their shields. This led to vests embellished with the same design that would be worn over the armor. Soon even horses were wearing a sort of dress with the knight's coat of arms emblazoned on it. Eventually these designs were registered and the rights were inherited by the oldest son of the family. Junior members could use the design by merely changing the crest. Perhaps the San Pasqual Trussells would have used a dairy cow.