I was just kidding...really! But the question actually comes up frequently, usually asked by those that are starved for attention.
As far as being seen, forget it! Headlight modulators, high beam during the day etc are tech answers but it really comes down to roadcraft. Many of the drivers out there are numb from the neck up and wouldn't see or hear you if you were driving an M1 tank.
"Loud pipes save lives" is a hotly-debated topic, but for my money it won't help much in the situation you describe as the noise is pointing the wrong way. Shoot, people can't even hear firetrucks and ambulances behind them!
Loud pipes only attract attention and annoy the people behind you and a bit on the side of you.
The people that need all your attention are the ones in front of you and loud pipes will not help there.
You want attention from the people in front of you?
1. Change your horn out to the FIAMM air or electric horn ... 129 decibles, under fifty bucks!
2. Get a headlight modulator, the blinking will drive them nuts better than a loud pipe.
3. Wear bright colors, black is the worst color to wear.
It has been mentioned before and I will mention it again, ROADCRAFT, predicting what an idiiot will do before they do it.
Welcome. Ride well and be happy.
Loud pipes do not save lives, they only annoy people. Low frequencey sounds are not as directionally propogated as high frequencly sounds and human ears are not adept at picking out their source. So when you BRAAAAAAAAAAPPPP - Fart- Fart Fart your loud-ass pipes, Joanie CellPhone isn't going to know where you are any better than if you were riding with stock pipes. She'll be a little alarmed and may just drive more erratically, which is the last thing you want.
Did you take the MSF class? Remember, it's your job to avoid getting killed while you ride. As soon as you think otherwise, you're doomed; and no pipe can change that.
I don't think the M4 is TOO loud, it sounds fantastic on gen 2's. (two of my buddies have them). It's kind of a 'tastefull' loud-as in loud in a Ducati kind of way
As for being 'seen', clothing does more then exhaust, exhaust helps a bit for pedestrians. If your exhaust is TOO loud, people can get annoyed on the 'slab and make a point to pass you when they normally would not. Being seen has to do with lighting, lane position and lane choice at certain times. Intersections can be dangerous, but the right lane in merge areas is a LOT more prone to being cut off by people making dumb last minute signal-less changes.
Probably most likely areas to not be seen in order of frequency/danger:
-Merge lanes: people make quick glance, last minute distracted decisions across multiple lanes. At intersections at least they pretty much HAVE to look every time to make a decision. Right lanes in merge area have two main dangers, being cut off(its amazing how desperate driver become of something so STUPID as missing an exit). Also, if you don't OWN your lane by position, people can also 'squeeze' your lane by accident thinking there is an opening. Center or left lanes are MUCH safer. If you are in the second lane from the right and the right is moving much slower then you at a merge area, you are asking for all kinds of trouble by going more then 10-15 mph faster.
-mall parking lots: are like death traps of stupidity. Often everything is slow non-fatal speeds but you can probably run out of fingers to count on for near-misshaps within 2 minutes riding in a mall parking lot from people and cars. At slow speeds it can also be very difficult to to make a panic stop without dumping the bike with no gyro effect to help you crank the bike in a quick turn. For some reason pedestrians brain's cramp as well when it comes to dealing with a motorcycle over a car, almost like deer.
-4 way stop signs: People blow these all the time because its two main roads meeting instead of an obvious side-to-main road stop. Big time check mirrors behind you and the intersection itself, also see lots of dumb U-turns.
-the 'standard' intersection with lights: the standard dumb u-turns, indecisive yellow light panic breaking by someone inf front of you, getting rear ended, you name it. Most intersection issues go smoothly if you have a vehicle to the right of you going through it for your maximum visibility. I tend to speed up or slow to keep one nearby if possible. At lights when stopped always be in gear and check your rearview mirror until traffic settles behind you, and when making rights stay far enough in the lane center to keep people from 'squeezing' you before you turn.
-secondary-residential road 'left turners' and driveways: people tend to get a little lazy around home from the routine. I really have hardly anyone turn if I stay left of center and stay with normal traffic limit speeds. You are asking for HUGE trouble speeding here over almost anywhere else. Everyone pulling in or out in these areas have made these turns HUNDREDS of times and really do not pay attention to your speed. (You will also find most 'lost' people in this area because there's nothing but street signs for them to look for-passing people 'hovering' to make a turn can be very dangerous if they change thier mind quickly when thier spouse yells NO NOT THIS ONE) If you are going too fast they often simply distance judge and turn, and tend not to speed judge oncoming traffic, once they are on the 'home stretch' they drive more by habit then being fully alert. In their head the drive is already 'over' while being within a couple hundred feet from home.
You can learn a LOT about riding when you are in your car as well. Of course people do 'stupid' things but if you watch carefully its the SAME stuff over and over. When you first start 'duking' it out in traffic on a bike you can have a little bit of a brain overload from the level of focus it commands. When you drive the car later you notice how EASY it is to drive it. Turn your radio off and watch traffic patterns. Merge areas have the same issues all the time, and things like a non-turn-lane left turn on a two lane(each way) fast road. You do NOT want to be so close behind someone that you can not see a left- turning car ahead if the car in front makes a fast lane change, nor do you want to be stuck behind someone turning dead stopped in a 55mph zone-not to mention being in the right lane when said car decides to come over. You can usually ride in traffic with enough cushion and lane planning that you hardly ever have to even brake hard at all with practice. That also doesn't necessarily mean putt-putting around either, sometimes you need to 'earn' your cushions by being a little faster instead of slower. If traffic is spooking you, take the car out for a spin and just WATCH what goes on.