Actually, proper firearms training emphasizes NOT walking around with your finger on the trigger unless you are about to shoot something, to minimize the risk of accidental discharge.
http://www.thetruthaboutguns.com/2010/08/robert-farago/the-secret-life-of-trigger-discipline/
This site often praises movie/shows that show proper trigger discipline:
http://www.imfdb.org/wiki/Collateral- for instance, see the comment on the photo 2/3 of the way down on the Glock 22.
On a different subject, whoever picked those pants for Cassandra ought to be shot - they made her ass looks 3 sizes too big.