SARAH: In Shakespeare's time the clothing of the upper classes literally proclaimed their social rank. If you were lucky enough to attend some sumptuous social function at the court, you did not need to recognize individuals to know their social status, all you had to do was see what they was wearing.
RALPH: For example here are some provisions from the Statues of Apparel that Queen Elizabeth proclaimed in 1574: only the immediate royal family could wear purple silk, gold cloth or sable fur; except for dukes, marquises, and earls who could use those materials in certain types of coats, cloth linings, or their hose; or if you had been awarded the Order of the Garter you could wear one specific cloak of purple. And these restrictions went on for pages.
SARAH: So Polonius's advice to Laertes about his clothes isn't simply a recommendation to look nice — Laertes must dress according to his station, both as a matter of family pride and also to communicate his social rank to others around him.