Surprised no one has mentioned this news item (capitalization is mine):
"Prince William's royal coat of arms was revealed Sunday and included a
unique addition--a tribute to his late mother, Princess Diana.
"The coat of arms...incorporates aspects of the royal arms used by Queen
Elizabeth II and Prince Charles IN ADDITION TO A SMALL RED SCALLOP SHELL
DERIVED FROM THE SPENCER COAT OF ARMS.
"The escallop motif, used by Princess Diana, has been borne by the Earls
Spencer since the 16th century and was a popular symbol for medieval
pilgrims."
Sir Winston Churchill's coat of arms had several scallop shells. Do you
know of any others?