Gibbs, Tony and Abby, while fooling around with facial reconstruction software, create a likeness of Dr. Mallard; the image shows actor David McCallum as he appeared on The Man from U.N.C.L.E. (1964).
If you look quickly enough while Gibbs types his password into Tony's computer at the start of the episode, we can see that Gibbs's NCIS clearance userID is 'lj_gibbs_NCIS'.
The NCIS Shooting Range is seen for the first time.