PA state law...
David Weaver
you can trim any part of a tree that overhangs your own property without notification or consent of the property owner that said plant/tree/etc grows from.
In this case, the hedges grow in my fence (which as is usually, is a couple of feet inside the property line to avoid issues with who owns the fence) and the branches grow toward my side to seek sun. If some of them overhung the adjacent property, I wouldn't be at all offended if every bit of them was cut, even if the effort was, shall we say, a bit aggressive.
The background is that Dippy in this case had four bushes of his own (large ones) next to the fence, which someone probably planted for additional privacy. He was apparently looking for a leaf free yard, which is a tough find here where any unoccupied area is hilly forest and you will find the odd January day where your leaf free property sees a big wind and every low area is filled with leaves.
I guess he was motivated as he removed every shrub and tree on his property and he was looking to extend his reach, and he probably hadn't considered that the fence was not the property line. He stated to my wife (who also would like a lawn that looks like a carpet and thinks trees are dirty - sometimes -I think she'd have a different idea if she wasn't able to sit under them) that it would be nice to get rid of everything, and she suggested I should be conciliatory and if he didn't like the hedges, that he could cut them out. Coming from a rural area, I mentioned to her that the real issue here is that I don't want to sit in my back yard and stare at him all day, or have his dog barking at us from its yard (which was common), and that the privacy was important, but also that we'd have a strange looking rose of sharon hedge on two sides and a bare fence in the back.
So, that's the whole story.
I'm kind of a rule follower when it comes to local or state rules - follow the rules. If you don't like the rules, lobby to get the rules changed in a transparent way - maybe others will agree. My maple tree grows over my neighbor's house. It's technically his responsibility to deal with the limbs, but since it's my tree, I would pay to have it done. He doesn't want it addressed as it shades part of his deck, so we're in a happy medium.
Dippy since moved away to a new community where there are no trees, so I think he's happy until the planted trees grow. My maple sharing neighbor isn't a fan of his because of the twice a day gas leaf blower in the summer, and the fact that at one point, he got upset with someone who cut him out of a plastering job and he swore on the phone. The hedge cutting savant called the police who arrived and informed him that they received complaints about someone "swearing all the time and possibly drunk". This is inaccurate, but I guess if you're looking to get the police out, you do what you need to do? They left as soon as they came, but it sort of set the tone.
I'm in your boat - the real point was that I like the hedge and don't want it cut. And it's mine. IF the neighbor had that big of an issue with the leaves, I"d have gone so far as to offer to remove them from his property when they fell, because...well, they're from my bushes and it's not that difficult. The point of the letter is less starting a legal process (and would've come from me and not an attorney), but to avoid the entire situation that could follow - it would establish that he was aware in writing that the ROS wasn't on his property and hopefully avoid any cutting. If he didn't like that, then there's nothing I can really do about that, but I do not agree with ever involving courts and police where they are not necessary. I guess they are sometimes needed, but I'm descended from PA germans and we generally try to solve things by compromising as individuals.
If I were going to cut limbs on a tree that overhung my property, I am not obligated to tell anyone, but I would do it anyway, and would also avoid making someone else an imbalanced tree.
I guess this topic sets me off a bit because my wife described the situation as the hedge savant considering cutting the hedge the day he was finishing his other bushes. He was just an odd guy to me - I'm sure I'm odd to some people, but I do tend to have a stubborn reaction when someone comes along with "that's what the law is, but we're doing something different here and I'm going to tell you what it is". I have a feeling that dippy on the other hand didn't even think about it and figured that if something so much as caused him to lift a finger, he had the right to remove it, and like many first owners probably think, he probably assumed the fence was right on the property line. We've got a much better neighbor now. Poor guy is from Turkey and when he first moved there, he had 10 different fertilizers and chemicals that the prior owner told him he'd have to buy. It must've been $1000 worth of stuff that he bought for a fraction of an acre. He (new guy) just wanted to know how often he should mow his lawn and why it was growing so fast, and he opened his shed door and said "I've been reading on the internet, and the guy I bought the house from gave me this list and said I needed to use all of these on the lawn, but I can't find anything on the internet that says the same thing. he said that the lawn would probably die without them". The shed shelf looked like a store display of bagged lawn treatments 
A little bit less commercial agriculture on the lawn for the neighbor and he isn't fighting a stalling lawn mower now. And he doesn't want to cut my hedges and thinks the idea that they create too much work is ridiculous. it all turned out well. He doesn't call the police, either.
