Since the loop antenna is a directional antenna and would be unsuitable for mobile two-way communications, I'm wondering if the loop on the police car was simply "Hollywood?"
The directional characteristics depend on the
polarization of the transmitting antenna. With
a low dipole using NVIS, the loop has little
directivity.
Even on ground wave, the null of a loop is
relatively narrow, so with random orientation
you probably still get at least 90% coverage.
After all, ferrite loops with a similar pattern
are used on AM BC pocket radios, and loop
antennas were built into most table radios.