All crew can know that the Syndicate have methods of getting equipment to the station, also known as “Uplinks”, but not where those uplinks are.
PDA uplinks
Security can open PDAs while someone is brigged, and can gain IC knowledge that PDAs contain uplinks if an unlocked uplink is found in a PDA.
For PDA searches see:
https://forum.spacestation14.com/index.php?/topic/2216-abnormally-through-searches/&do=embed
Radios
Radios are suspicious enough that crew can “inspect” them and discover that they are uplinks if they mange to operate them.
Using uplinks
https://forum.spacestation14.com/index.php?/topic/2233-use-of-contraband/&do=embed