  The current explosion in detection and characterization of thousands of
extrasolar planets from the Kepler mission, the Hubble Space Telescope, and
large ground-based telescopes opens a new era in searches for Earth-analog
exoplanets with conditions suitable for sustaining life. As more Earth-sized
exoplanets are detected in the near future, we will soon have an opportunity to
identify habitable worlds. Which atmospheric biosignature gases from habitable
planets can be detected with our current capabilities? The detection of the
common biosignatures from nitrogen-oxygen rich terrestrial-type exoplanets
including molecular oxygen (O2), ozone (O3), water vapor (H2O), carbon dioxide
(CO2), nitrous oxide (N2O), and methane (CH4) requires days of integration time
with largest space telescopes, and thus are very challenging for current
instruments. In this paper we propose to use the powerful emission from
rotational-vibrational bands of nitric oxide, hydroxyl and molecular oxygen as
signatures of nitrogen, oxygen, and water rich atmospheres of terrestrial type
exoplanets highlighted by the magnetic activity from young G and K
main-sequence stars. The signals from these fundamental chemical prerequisites
of life we call atmospheric beacons of life create a unique opportunity to
perform direct imaging observations of Earth-sized exoplanets with high
signal-to-noise and low spectral resolution with the upcoming NASA missions.
