Another mechanic I really like comes from Dungeon World, where the alignment you choose isn't so much a wide open philosophical statement, as much as it's a declaration that "this alignment + this class + this specific behavior = marking XP."
Other games that I enjoy have a mechanic for awarding something for a predetermined roleplaying trait or story role that a character might have. I have noticed, however, that some of these mechanics, despite being made to engender roleplaying, sometimes don't get used as often as they could. I think this may be because, even in very clear circumstances, some of these guidelines call for some degree of interpretation, and many players either don't want to ruin the flow of the game by asking the GM for a "ruling" on if the benefit should come into play, or they just don't want to assume that they know what qualifies if there is any doubt.
That leaves rewarding the mechanic solely on the GM, which can be problematic, because it's one more thing the GM then has to track in his head on top of everything else he's doing.
Thinking about Marvel Heroic and Milestones and Dungeon World and alignment, I started to think about what some of the "roleplaying for additional benefits" rules would look like if spelled out in a more "cause and effect" manner. Here are some of the examples I came up with.
Dungeons and Dragons 5th Edition
The following uses background elements from the Refugee background found in Goodman Games Glitterdoom adventure.
Personality trait: I refuse to quit no matter how difficult things may seem = When you advocate moving forward when more than one of your companions advocates retreat, gain inspiration.
Vigilance: One must constantly be on the lookout for danger or difficulty, and swift to intercede before it comes to fruition = When you volunteer to take watch or go on patrol even when something else might be easier or more advantageous to you, gain inspiration.
Bond: A kindly soul helped me when I most needed assistance and I’ve vowed to return the favor whenever possible = When you provide assistance to someone that obviously cannot repay you for your deed, gain inspiration.
Flaw: Having been bitterly disappointed in the past, I’m reluctant to trust others = when you refuse to accept help from someone that you do not know, gain inspiration.
While the above may not be quite as open for gaining Inspiration as leaving the individual traits and they stand, they do clearly show what the PC should do in order to earn their reward, and it makes the process of asking the GM what qualifies a lot faster and more efficient.
The following uses the Demeanor mechanic from the Deathwatch game as an example.
Calculating: The Space Marine’s mind is highly analytical, constantly aware of the pros and cons of
any decisions he faces = whenever the Space Marine allows his allies or enemies to go before he would normally act in order to more fully assess the situation, double the benefits of triggering this Demeanor.
Gregarious: The Space Marine is a charismatic and talkative sort, one who puts his Battle Brothers and even normal humans at ease = whenever the Space Marine is clearly not taking any other actions other than attempting to communicate in an amiable manner, double the benefits of triggering this Demeanor.
Hot Blooded: .The Space Marine is quick to temper and aggressive in all things = whenever the Space Marine's actions are a surprise even to his companions and are not discussed before they are declared, double the benefits of triggering this Demeanor.
Studious: The Space Marine values lore and learning, preferring to think his way through a problem = whenever a Space Marine spends an action making a Lore check to recall a situation similar to the one currently presented to him, double the benefits of triggering this Demeanor.
Taciturn: The Space Marine is a brooding individual, little given to conversation = whenever the Space Marine takes an action and communicates his intention non-verbally and without consultation or advice, double the benefits of triggering this Demeanor.
Pious: The Space Marine cherishes faith in his Primarch and the Emperor above all = whenever the Space Marine extols the virtues of their Primarch or the Emperor and relates why their action exalts the same, double the benefits of triggering this Demeanor.
Stoic: No test of endurance is too much for this Space Marine = whenever the Space Marine attempts a check that may cause him to suffer detrimental effects after he has already done so in the same encounter, double the benefits of triggering this Demeanor.
Scornful: Pity has no place in this Space Marine’s heart = Whenever the Space Marine continues with a course of action even when extenuating circumstances might make others hesitate or reinterpret the situation, double the benefits of triggering this Demeanor.
Ambitious: This Space Marine’s gaze is ever-lifted towards his goal = whenever the Space Marine attempts a course of action that results in a negative penalty to his check, double the benefits of triggering this Demeanor.
Proud: Dignity and honour are important to this Space Marine = whenever the Space Marine attempts an action that he can tie directly to another prestigious action that he was involved in, double the benefits of triggering this Demeanor.
Star Wars--Edge of the Empire
This example uses Edge of the Empire and it's Motivations as an example of "Milestoning" an element.
Specific Ambition--Friendship: The character seeks to be liked by others and goes out of his way to make a good impression. He may or may not be gregarious, relying on his actions and deeds to foster friendship = Whenever a character takes makes a test to improve the reaction of an NPC solely for the purposes of making that NPC like the character (i.e. no other benefits are sought from the character), gain 1 XP. Only 1 XP can be gained per scene in this manner, and no more than 5 XP can be gained per session in this manner.
As the GM, you probably aren't going to want to go through every single roleplaying descriptor style mechanic in the game and redefine them in the "milestone" format. There are going to be tons of elements your PCs may never even touch.
However, once your players start to chose these elements, if everybody is game, talk with them about defining the elements in "milestone" format to make things clear for everybody. Let them give it a try writing them out as milestones, if they want, or you can if they aren't comfortable, then agree, together, on of the final milestone sounds workable.
I haven't had a chance to use this in a game yet, but it sounds as it if might be a really interesting way to get some of these roleplaying boosting elements to see more active use in a campaign.