A magus carries a spear (not his talisman).
Is the spear covered by his Parma or does it "stick out"?
Judgement call.
Elements of the rules support both interpretations. Usually(?) anything "worn" is covered. And one short step from "worn" is "wielded".
That, tho', creates some problems - if you pick up something small and close your hand around it before a spell hits, does Parma protect that? What if it's larger? How much larger? What if you pick up a grog and wrap your cloak (that you're wearing) around them?...
Judgement call.
Covered in this case. I agree with the hound that this is a slippery slope, but a spear doesn't sound like abusing the rules
(I would not accept a rope held by the magus tied around the hands of 50 people)
I would say no, a spear is just too large. AM5 p.85 says Magic Resistance covers 'the maga, her clothing, and other items that are very close to her'. When you hold a spear, it is usually not 'very close to you, except where you hold it. Unless maybe the maga is keeping it straight against her body, and even then it is doubtful.
Besides, if you start ruling that it is covered, where will you draw the line ?
So, a maga w/ a dress and a long train has the dress covered, but not the train? Where would that line be drawn, indeed! 
(Which is why I decided not to post a definitive answer, even if "I" have one for myself - thought about it, but this is the type of thing best to leave to each SG/Troupe.) 
Where is your (personal) limit? Why? I'm kinda in the market for arguments for and against here 
In my saga, it would be covered by Parma as a possession. However, in my saga, possession is a category of the individual (see A&A p.22-23)... so anything an individual is holding or is adorned with is considered part of the individual.
My girlfriend is small - I can lift her without too much trouble and hold her for a good while. Does that make her part of 'Individual'?
(when I'm holding her, obviously)
...Mind you, I'd have to use both hands, so no gestures
Interesting question and a tricky one... but off hand, I would say no. She is another substance, sharing with you the categories of relation and action, rather then a category of possession. However, I can see making the opposite ruleing and some interesting implications as a result. Could be fun either way really.
I guess for a complete ruling, I'd have to dig out my Aristotle and I'm not sure which box I packed that in.
I don't have a personal limit - I have a personal philosophy. And that is...
The more definitions and hard limits you make, the more you have to make, and the worse the game and the story (can) get. So, if it's not critical, just don't go there.
The rule is: it's magic. It's not purely predictable. So don't push the boundary and you'll never cross it.
If a sword, why not a spear, why not a pike? If a pike, why not the tongue of a wagon?
If a dress with a train, why not a rope around your waist, or a kite?
Why not? Obviously - because that's abusive. Somewhere in there it's "crossing the line".
My players know what is "acceptable" - and that's more or less as described above. The spear is (usually) covered. If it's in doubt, then it needs to be with them when they conduct their Parma ritual - then it's clearly "part of them". No other living creatures.
And that's it.
Beyond that, it's like pornography - I recognize abuse when I see it, and so do my players (when they're being honest w/ themselves), so my players are usually reasonable. If they (accidentally?) stray, we talk about it, I make a judgement, and we continue.
If it helps, here is my 2 cents...
I look at the question of the "reach" of parma as a question of contagion and arcane connections. Basically, if an object is "gaining" connection with the magus as a possession being carried, it is also protected by the magus' parma. So what is actually in the mage's hand, at that moment is building an arcane connection with the magus, and so is protected. Their clothing, at least while being worn, is again reinforcing their connection to the wizard and therein is protected. A small object in the magus' hand has an ephemeral connection that once more is building the longer the mage carries it, and so it is protected. Something carried by the magus in the pocket of her cloak is also protected, as it is building up arcane connection to her. Something wrapped in her cloak generally is not. A person, carried or otherwise, is an individual in their own right and not a possession, and is also covered by the theory of forms (corpus) and thus is not covered unless I specifically extend my parma to them (and there are rules for that). If I was feeling particularly fast and loose, I might allow the girlfriend being carried to be protected by the magus' parma because it's "True Love" and therein she is arcanely connected to the magus, etc., but... In general, no.
...we're both Corpus, I assure you - much more alike than eg me and my clothes, if we go by composition.
That's a modern perspective. However, if you look at the pages in Arts and Academy which I reference, you will see that the Aristotlian prespective could be interpreted as being very different.
Here, here! (or hear, hear! I've never know which was the right one) 
Allow me to rephrase: we're both covered by the same Form (namely Corpus). Our clothes aren't.
This is the rule we use in my saga. Which is why I both refered that page and emphasized that my statement refered to my saga.
In the specific case, you and your girlfriend are two different Corpus individuals. Your clothing and hers are categories of your individual Corpus substances.
Edit: thanks, by the way, you've helped make this much cleared in my own mind. My players never ask good questions like this.
Reverse the question: if you hit someone with the spear, does MR protects the target?
Hear, as in ~that was worth listening to. Extreeemly vaguely that is.
I'm not disagreeing, I just need the reasoning
We should always be "group" yes?
Mine do, occasionally.
In this case "no" - nothing magical about the spear, no enchantements at all.
It has been specifically chosen in order not to be resisted.
I'm guessing your argument then is that it's not covered by his MR, because then that is a magical effect that should be resisted?
Please people, I'm still lookng for the reasons why (not)