The following entry is not finished, but it was looking at spending an eternity on my hard disk, so I am releasing it into the wild in the hope that you will forgive my rampant lack of clarity of thought.
I also would like to apologize in advance for mentioning TV Tropes & Idioms. If you had any willpower whatsoever you would not go there. I blame you, really.
I am shoving this here because I don’t know how to bring this up at TV Tropes.
If you were to generalise from there you’d get a meta or super trope called Obfuscating X, where a character will consistently adapt a trait or persona as a coping strategy.
In Are You Being Served the character called Mr. Humphries is Ambiguously Gay (also a trope). You could say that he pretends to be straight as a coping strategy in a part homophobic world.
Humphries, Murdock and Vila (the ‘weak’ characters in Blakes 7 were addressed using their given name) share a feature that TV Tropes does not mention and that yet creates a completely different trope: it is never made 100% clear whether these characters are acting, or whether they really are who they seem to be.
In other words, they are not just Obfuscating X, but also Ambiguously X.
Note that the characters I mention all seem to be something unheroic, deviant from the norm, or societally undesirable. They are also there to generate laughs (although I am not sure that this is necessary for the trope). Fans of the characters could be forgiven for hoping that the characters could one day be revealed to have been ‘normal’ all this time.
Also note that this is a different thing for Mr. Humphries than for the other characters. Vila Restal copes with being a coward and a kleptomaniac by pretending to be stupid. Murdock prevents becoming a wanted man by pretending to be insane. The ambiguity is not along the same axis as the thing that needs to be hidden, whereas it is with Mr. Humphries.
Having Ambiguously X characters is a powerful tool in the story teller’s box. I already mentioned the possibility to use them for comic relief.
Such characters also offer a writer the chance to create different perspectives:
* Vila Restal is often used for Through the Eyes of Babes moments (surely that is in itself a trope?). At one point in the episode Stardrive he even does so deliberately (one of those moments therefore where his alleged normalcy shines through). A dangerous repair must be performed, but he is the only who knows how to do it. The others though are not aware that he knows. So he waits a little, then feigns to be drunk and reveals the procedure in his drunken revelry: “Because my lovely Dayna, and Soolin, no one ever tells someone who is drunk to volunteer.”
As an aside, and with regard to Through the Eyes of Babes, Douglas Adams uses this technique quite explicitly in Dirk Gently’s Holistic Detective Agency in that the titular character realises that sometimes the simplest solution is the best one. When Dirk tries to solve a case, he goes out in the street and finds a small boy, and puts the problem of how the culprit dunnit before him. The boy responds something like “It’s bleeding obvious, innit? He must have ****** ******”, and then continues to kick Dirk Gently in the shin and walks off.
* The A-team uses an interesting twist. Murdock’s crazy talk is often followed by a segue by Hanibal who uses it to start the action. Hanibal does this in such a way that he at least casts doubt on whether Murdock’s talk was really that crazy to begin with.
* Mr. Humphries gets the laughs because being gay is ‘gay’. But he often turns things around, confronting the other characters and the audience with their bigotry. For instance, he will say something along the lines of having spent the night with a ‘friend’. One of the other characters, typically Mr. Lucas, will reply in a lewd manner suggesting that the friend must have been a male lover. At which point Mr. Lucas will reveal that the friend was a woman. Note that this too lets the alleged normalcy of Mr. Humphries shine through.
There is of course something deeply troublesome about using Ambiguously X characters, namely that there is a strong suggestion that there is something wrong with not being normal. One of the reasons this trope works is because it places sympathetic characters in a position where a prejudiced audience wants them to be taken out of, while at the same time giving that same audience the chance to revel in their prejudice.
The dangerous thing for the writer to do is to make the characters normal. This will give the audience a feel-good moment only once, but makes the characters unusable for the rest of the show, especially if their deviant trait was exactly what set them apart.