sic. To urge or incite to hostile action, as in siccing dogs upon someone. In a metaphoric sense, any time someone is ordered to go after another. There is an implication that the purpose is to do harm to the object of siccing, not simply to dissuade or drive off.

In the coverage of Winona Ryder's shoplifting trial, E! Online describes Saks security manager Kenneth Evans as “siccing the security cameras on her.”

Don't know sic 'em. This turn of phrase is used to describe a stupid person. While used in this shorthand form it is meant to imply a longer formulation: “doesn't know sic 'em from 'come here.'” The implication that stupidity is illustrated by an individual's inability to distinguish things that are obviously different or opposite is found in numerous colorful turns of phrase such as “doesn't know his ass from his elbow” or one of my father's favorites, the alliterative, “doesn't know shit from Shinola.” The lexicographer Peter Tamony is reported to have opined that sic 'em is a corruption of “seek 'em”

Figure 2 is labelled “confused dog” on The Pet Experience web site. I am taking the word of the experts that this is indeed an expression of confusion in the canine realm.