Hmm.. I still remain a big fan of typing "/tell MaybeANoob Hello! I don't think I met you before. Are you a new player?" and then taking it from there. I've had people reply to this and then ask me OOC questions about the game in /tells, and even had one who deleted and remade his character entirely once we'd talked about the RP in PS because he wanted to make sure it was a character he'd be able to role-play. The questions I have had in reply have mostly been intelligent ones in general either way, ranging from this example to the more basic "is this game good?" "how many people play?" "how much RP actually happens?" "is it really free or will I need to pay for the best items?" These are all questions someone might want to have answers to before learning too much about the annoying little details of how PS works. Why invest too much until you have an idea that you might want to stay?
And if they don't answer the /tell, that seems the best time to switch the OOC into main a little.(I use brackets when doing so even if alone with the 'noob' because it can never hurt to start off the 'brackets = OOC' association when used in main as soon as possible.)
Regarding everything Tessra said about types of RP and which are right/wrong - full and absolute agreement. This community would probably not feel quite so small if all of the little factions with their 'preferences' would just stop bashing each other and look for some common ground instead.
I'm largely in Tessra's position with regard to what kind of RP I do/don't like and one of the reasons I have mostly withdrawn from 'serious' RP is because I haven't been able to find any that consistently goes on in my timezone and all that I seem to find is tavern-talk and helping people learn how to do things. No plots with depth. It's hugely frustrating for me as an RPer, but I still always respond to people who approach me with these kinds of things. I would certainly never tell them they need to change their RP style in order to interact with me.
It's basic decency really and also because I recognise that people change how they RP and interact with others over time. I'd go as far as saying that, if approached by someone trying to RP, it's always better to respond IC to them, even if it's just an IC method of distancing yourself from that RP because you don't favour it - because you never know when that same RPer might instead do some RP you would like and which you otherwise might have on some level excluded yourself from.
If you don't like 'darker' themed RP, then it stands to reason you'll be playing a character who doesn't want to be tied up in those things as well. Have your character decide to limit their involvement. It doesn't take much to type "/me stares blankly at RandomBadGuy, excuses themself quickly and walks away" or even "/me looks carefully at RandomBadWoman, then looks away and continues with blahblahThingTheyWereDoing." It can always be accompanied by a quick /tell just to make sure it's understood, but it's easy to acknowledge an RP without it overtaking your own.
Quick edit - Pakarro, that is exactly what I'd be in favour of. I have often used low level alt characters to 'help' people from and that would really fail if a had a big flashing NOOB sign over my own head at the time.
Let it be an optional selector on character creation if anything at all.