If you’re that worried, you could always engrave your last name somewhere visible, or use a cable lock to secure it to the LATCH point. The engraving might deter a thief and the cable would stop an unprepared, smash-and-grab (though, only after he busted out your window).
You have no idea what a pain in the butt a car is in Manhattan. Parking on the street means moving it every day, and it will be broken in to. The insurance is high, and then there’s winter. Really, renting a car on a couple of weekends a month is cheaper. You take the train out of town and rent it at a station in the suburbs.
The OP is asking for a miracle. I grew up in NYC and moved back for five years for work later on. If you leave anything visible in the car you will get victimized. I left the cables for my portable CD player and radar detector in my car. They smashed my $175 window to steal twenty bucks worth of cables that were worthless at the pawn shop. My radar detector and CD player were safely in my house. The answer, which he doesn’t want to hear, is that the seat has to get taken out every day. Put it in the trunk or put it in the house. If you leave it in the car it will eventually generate unwanted attention. Yes it stinks that you have to go through the process of properly securing it every time you need to use it but it beats having to buy a new one and maybe having to replace a smashed window.