The Enterprise visits the planet Mintaka III in this episode. Mintaka is also the name of the Westernmost star of the three stars that form Orion's belt in the Constellation Orion. It is a white-blue Super Giant star located approximately 900 light-years from Earth, and is over 20 times larger and 7,000 times brighter than our Sun.
The title is related to the phase Quis custodiet ipsos custodes, a Latin phrase from the Roman treatise Satires of Juvenal, written around AD 100, variously translated as "Who watches the watchmen", "Who watches the watchers", "Who will guard the guards", "Who shall watch the watchers themselves", or something similar. Another Juvenal expression provided the title of Star Trek: Bread and Circuses (1968).
Ray Wise who plays Liko, is searching for Dr. Palmer and "the Picard." A year later Wise began to appear in Twin Peaks (1990) as one of his most famous roles, Leland Palmer, who knows a family named Packard which sounds a bit like Picard.
The "who watches the watchers" quote is sometimes incorrectly attributed to Plato. Although one of his debates in The Republic has a similar theme, he never writes anything that could be translated into that line specifically.