In The Merchant Of Venice, what proper honour is given to Arragon to indicate that he is a prince?

The Prince is one of many suitors who came to Belmont to chance their luck at winning Portia's hand in marriage by choosing from three caskets: gold, silver and lead. In terms of her father's will, Portia must marry the one who chooses the right chest. She is not much impressed with the line of suitors but has no choice but to adhere to her father's wish if she wants to inherit his estate.

Portia expresses her disdain for the Prince by mentioning the following:

Ay, that's a colt indeed, for he doth nothing but
talk of his horse; and he makes it a great
appropriation to his own good parts, that he can
shoe him himself. I am much afeard my lady his
mother played false with a smith.

She and Nerissa refer to him as the Neapolitan Prince and Portia clearly believes that he is obsessed with his horse and he quite likes the idea that he can shoe the animal himself. She, however, affords him the proper honour as befits his title when he arrives to make his choice, in both the manner in which his entrance is announced and in her address. Firstly, there is a flourish of coronets and secondly, she refers to him by his title:

Behold, there stand the caskets, noble prince

She also refers to him as 'my lord' indicating her respect for his position.

The Prince refuses the lead casket since he is not prepared 'to give and hazard all he hath' and he, likewise, rejects the gold casket for he deems himself different from the multitude since the inscription reads 'Who chooseth me shall gain what many men desire.' He deems himself special and does not subscribe to the idea that he is so common as to fall for gold's glitter. 

He decides on the silver casket and is disappointed since he has made the wrong choice. The inscription reads:

Who chooseth me shall have as much as he deserves.

The Prince is then confronted by a fool's head when he opens the casket. To add insult to injury, the inscription calls him a fool who arrived with one fool's head but who will now leave with two. The Prince, obviously upset, leaves immediately with his train of servants and followers in tow.