source: http://www.scienceagogo.com/news/pulsar_et.shtml

Sagan said that it is unnecessary to create the pulsars themselves in
order to take advantage of their communications potential. "Has anyone
examined systematically the sequencing of pulsar amplitude and
polarization nulls? One would need only a very small movable shield
above a pulsar surface to modulate emission to Earth. This seems much
easier than generating an entire pulsar for communications. For
signaling at night it is easier to wave a blanket in front of an
existing fire than to start and douse a set of fires in a pattern which
communicates a desired message." Sagan was always such a smarty-pants,
particularly in the context of the recent discovery of a maser
modulated pulsar.