Disclaimer: I despise this administration, and think ICE should be abolished.
I would assume they mean that cops have a general duty to prevent/catch crime. So all you're doing by notifying people with waze or head taps is saying "hey there's police there!" Which everyone has a right to know.
However, because ICE is specialized, warning people of their presence might be seen as more akin to attempting to warn someone that their house is about to be raided by the FBI
