Obvious cyberlimbs are obvious.
Funny, Page 344 of SR4A says that they are imminently recognizable... Unless covered by clothing.
So, don't allow them to be covered by clothing?
Keep reading.
In some cases, they are glaringly obvious and outlandish. This
tends to affect the character’s social dealings.
Perhaps dropping 2 B/I armor into a hand or foot is one of those cases?
If you didn't think it was outlandish, then you wouldn't have brought it up.
There's no realistic way that a hand can provide 2 points of ballistic and impact protection and look normal.
The limb would need to basically be a hardpoint for a long shield piece traveling proximal from the wrist or ankle.
Consider that the previous sentence is
They are often chromed or matte colors but visibly mechanical in nature.
It's clear they're talking about stuff like the cosmetic mods in Augmentation where you can cover it pink neon lights depicting lewd acts.
As for the armor, it's internal. Otherwise, you couldn't armor synthetic cyberlimb and still have people have to make Perception (3) tests to spot its artificial nature. It also explains the fairly large amount of capacity it uses up.
Also cyberlimbs should be fairly common in any era of shadowrun. They were suppose to be the go-to fix for a host of limb issues. Docks workers are suppose to be cybered enough that they don't use lift suits anymore. Thematically, they also fit it quite well even considering SR's shift from cyberpunk to post-cyberpunk. In older editions, they represented how people had to give up their humanity to keep with the cutting edge. In the current edition, they represent that have metal arms are cool and are way awesomer than normal human limbs.
We would have see way more characters using cyberlimbs over the years if it wasnt' for the fact that they sucked so horrifically that no one touched them. I'm not saying everyone has one, but it should be a decent enough percentage roughly like that of trolls or dwarves (2% each).
I also think it's unlikely for people to freak out even if they did know they were armored limbs. First off, it's perfectly legal. You don't even have to buy a fake permit for it. Secondly, consider the wealth of armor and how even messengers can wear 6/6 jumpsuits, I think armor wearing is quite common. After all, this is a world were there are dogs that look like men and go on murderous rampages during full moons and violent gangs can operate in the fairly nice parts of downtown Seattle.
Balancewise, the issue isn't that mundanes can have a ton of armor. That's one of the few things mundanes have going for them. It just really kicks the other defensive ware options to the curb. You should become tough because you replaced your bones with metal like Wolverine or have kelver for skin and not because your doctor chopping off your hands and feet due to you coming down with diabetes.
Since bone lacing, othroskin, and dermal plating are a tad on the weak side regardless of the state of cyberlimb armor, I'll be for buffing them and then nerfing cyberlimb armor. My quick and dirty suggestion is to double the effectiveness of the defensive ware and then have cyberlimb armor on partial limbs only apply for that limb. This also will tend to increase the essence cost of being defensive enough that mundanes don't really care, but mages will. Thus it helps keep mages lower defenses relative to combat focused mundanes, but cybermages can still totally exist.