If it’s done digitally, it’d just be replication of packets. No sign at all if you don’t capture the code or the duplicated traffic.
Has NYC upgraded all of their equipment to be digital IP based?
I wonder if the discovery of the "tapping" was made partially in upgrading President Trump's communications security lines (encryption, etc). I know he was issued a special secure mobile device (as Prez).
A top secret level security system & specialists verifying its installation/integrity would have to know all of the equipment in the loop.