You need to remember that running silent is not the same as invisibility.
Icons that are in close vicinity of you are so bright and clear that you automatically spot them. You can tell what type of icon they are by just glancing at them. Further away icons get less bright and less clear the further away towards the horizon they are. You might even need to look at them in detail before you can interact with them or even before you can tell what type of icon they are. If you see a vehicle 600 meter down the street you need to focus for a second or so to filter out it's device icon in the ocean of other icons around it. At this distance you also get a negative dice pool modifier of 1 dice due to noise (unless you have a datajack or run signal scrub). But even so, once you know what you are looking for you only need one single hit to spot it. It's icon is still as obvious as a neon sign, running crowd, yelling or gunfire would be for a meat space perception test. The matrix is helpful at finding things.
Devices that run silent limit their traffic which make their icons dim and flickering and harder to spot, but they are far from invisible. It is actually not very hard at all to notice that there are icons around you that are limiting their matrix traffic. In fact if you set your commlink to filter so that you only see flickering and dim icons in your vicinity then you will see every single one of them with a single hit from a perception test. To notice that there are silent running icons in your vicinity is as easy as spotting a neon sign, running crowd, yelling or gunfire for normal perception.
If you walk up to a camera you will either see a bright and clear device icon that you automatically can interact with.... or you will see a dim and flickering device icon that you first need to study in detail before you can interact with. In this case you know which icon you are interested in. You don't need to randomly pick any of the other dim and flickering icons around you. But before you can hack the icon that belong to the camera you are interested in you first need to take an opposed matrix perception test. Most silent running device icons only have a device rating of 2 and don't even have a sleaze rating which mean they are very easy to spot. Some might be slaved to a Host which potentially make them very hard to spot, but if everything fails you can often just walk up to the device and establish a direct connection with it.... Also, while inside a host all silent running devices out on the grid that is part of the WAN will also show up clear and bright (no matter where in the world they are located).
Once you spot an icon that is running silent you will have it in your "recently spotted icons"-list if you will. No matter if it change icon or travel to the other side of the world or to another Grid, but you will lose track of the icon if it reboot or if it successfully bend the matrix by using the illegal sleaze action Hide. In that case you need to spot it again, but it should not be too hard since you know what you are looking for...
