Shadowrun 5e core rulebook states at page 235:
If you’re trying to find an icon that’s running silent (or if you’re running silent and someone’s looking for you), the first thing you need to do is have some idea that a hidden icon is out there. You can do this with a hit from Matrix Perception Test; asking if there are icons running silent in the vicinity (either in the same host or within 100 meters) can be a piece of information you learn with a hit. Once you know a silent running icon is in the vicinity, the next step is to actually find it. This is done through an Opposed Computer + Intuition [Data Processing] v. Logic + Sleaze Test. If you get more hits, you perceive the icon as normal; on a tie or more hits by the defender, it stays hidden and out of reach.
Note that if there are multiple silent running icons in the vicinity, you have to pick randomly which one you’re going to look at through the Opposed Test. Marks can’t run silent because they’re already pretty hidden, but all other Matrix objects can be switched to silent running by their owners.
At the same time – under Matrix Perception sidebar on page 235 it says:
When you take a Matrix Perception action, each hit can reveal one piece of information you ask of your gamemaster. Here’s a list of some of the things Matrix Perception can tell you. It’s not an exhaustive list, but it should give you a pretty good idea about how to use Matrix Perception: If you know at least one feature of an icon running silent, you can spot the icon (Running Silent, below). The marks on an icon, but not their owners
Now, questions. Imagine following situation – some decker, who had bought a hundred of RFID tags (1 nuyen each) and set them to running silent (or even stealth RFID tags, that are running silent by default (10 nuyen each)) and goes to perform some hacking. The target is protected by security decker.
Question 1. Security decker rolls his matrix perception to look for silent icons and gets at least one hit and finds out that there are running silent icons nearby. Does he get an exact number – there is 101 entity (100 silent RFID tags and one decker (who has, probably, more than one device, but they are likely to be panned and be represented as one icon) hiding nearby or just that there are hidden entities?
Question 2. Is there any way to focus on decker, not on RFID tags, when trying to reveal silent icons? I.e. does ‘persona’ counts as feature of icon?
Question 3. What counts as feature of icon?
Question 4. Decker used Hack on the Fly action feature and succesfully left a mark on device he is trying to hack. Security decker used Matrix Perception to check on device and scored one hit and can see decker’s mark. Can that mark be used to narrow search for that decker?