That's a large part of the reason I don't make too many visible modifications to my bike. I don't feel like being hassled by the law over something like turn signals. (That, and I'm not one to spend money on purely cosmetic modifications to my bike, to be honest.)
On the other side of that, I'm all about aftermarket stuff that makes me safer. I've considered adding a taillight flasher to mine, because I find that people seem to notice them more.
Overall, though, this is the kind of stuff that I think shouldn't garner much attention from LEOs. It also happens to be the kind of stuff that I hear about guys on sportbikes being pulled over for every day.
On the loud pipes thing, I'll jump in there. I have no problem with aftermarket exhausts, within reason, but there are some systems out there that just make ridiculous amounts of noise. If your pipe is so loud that it makes my ears ring when you ride by, I think that's taking it a little too far. I also don't really believe that a loud pipe helps make you all that much more noticeable to cagers, as most people can't tell which way the noise is coming from, and the modern car has enough sound deadening and interior noise generators to drown out all but the loudest, most ridiculous pipes.
Now loud clutches, that's a whole different story.... 