It is.
Pretty fun, can lead to some awkward and rather hilarious situations.
Basically, you have a target, just like everyone else. Pull out a weapon in view of security or with witnesses around and you'll be detained for a bit and lose cash and items in inventory. Cash is rewarded for kills; amount varies with weapon used, so it pays to snoop around for high rewarding ones or go for high damage for easier kills (usually pay less).
Trick is not getting caught hitting your mark, without getting wacked yourself.