NY MTA to NYers:
No searchee, no ridee.
Being "public" transit, and thus not being a "privilge" (the excuse they use for driving) or a private airline ... I wonder how will this would hold up to a legal challenge.
And what if you have alrady paid the fare and you refuse once inside ... they would have to have some kind of refund mechanism. Putting up a sign in a public place doesn't make it so.