I decided to expand on this idea, and here's my idea of it all.
I understand some of this will require a client change, but... fair enough.
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Introduction: Every character will have a hidden number which represents how many nobility points he or she has. These nobility points are used to gain 'nobility levels', and increase and decrease depending on factors as below.
Noble Levels: To increase a level, you need to gain enough points. The amount of points isn't static, it instead tries to keep things in a bell graph fashion (with 'commoner' in the middle). However its calculated separately for each race (so as to not disadvantage some races over others). So for each race you would have mostly commoners, but then a few nobles. The levels are:
Serf , Commoner, Lower Nobility, True Nobility, Blue blood.
Obviously these names may be different for each race, as is the perception of them. Ascension/Descent to a level needs at least 3 RL days; so you wont be talking to a person who suddenly turns noble.
Increasing the Level:
Below are some actions/items which can increase the level, there's also a 'cap' which is how much (maximum) they can give you each day if you have the best of the best. Moreover, willpower helps increase the amount.
Items: The most obvious way to increase nobility is to dress up like a noble. Wearing clothes will (each cycle) increase your nobility up to a certain cap, the cap depends on the quality of the clothes multiplied by their state, multiplied by a value which is different for each item.
Clothes should also degrade, their state should go down over time, HOWEVER the only thing that will be lost will be nobility points, nothing else. So if you're a mage who bought a new wardrobe of clothes for the alledged bonus to magic, they'll still give you the same bonus, even when they turn tattered. Clothes keep the same quality though.
Jewlery works in the same way (no degradation though), and the above helps encourage fighters to take off their armor from time to time and stay wearing (expensive) clothes

Cap: High
Good Food and Drink: Eating the finest foods available, and drinking the rarest wines is a good statement about your riches.
This gives a use to brewing, and also helps sales for expensive food.
Cap: Medium.
Sibanac: Arrr.
Cap: Low
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Also there is a limit (both upper and lower) to how many points you can gain or lose.
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Decreasing the amount
Obviously certain actions will reduce people's perception of your nobility.
Wearing rubbish clothes: Wearing low quality (bad or worse) clothes gives people a bad impression of you, and they slowly and gradually degrade the amount of nobility points you have. The amount depends on the (inverse quality * inverse state * a constant different for each item).
Cap: High
Eating rubbish food: Apples and other fruits make a good meal, but its not something a noble would eat.
Cap: Medium
Death: Self Explanatory
Cap: Medium
Crafting: (This may seem strange). A noble does not do any work, so its not a good image to see a person dirty himself with soot, or sawdust when he works like a commoner. Each finished good gives nobility a small kick down. This penalty is removed for exceptionally good work (think some sort of legendary swordsmith)
Time: Time should remove points on its own. -d(points)/dt should be dependant on how many points you have already.
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Use:
More Purchases possible: NPCs should have 2 sets of stocks, one which they sell to everyone, and the other only to important people. So for example if eliza has 3 metal gloves, anyone can buy them, but if a noble talks to her, he might be able to buy 5 instead, as she'd make an effort (checking in her stores ect...) to give an important person his wishes.
'Boss' Monsters: Some dungeons should have 'boss' monsters, which are reachable only through talking to an NPC ('servant of the boss') who then teleports them. The boss would only fight people of a certain degree of nobility, since the others aren't worth its time.
Housing: Nobles should be able to have larger houses then the others
Player Interpretation: The names (Someone 12345) should be coloured differently depending on the nobility. This shows that your character has noticed that the person is a noble from his actions and clothes; and is expected to RP it appropriately. The rest is left up to the players.
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Discuss.