Exoplanets of the Milky Way

Exoplanets are by definition located outside our solar system. By measuring variations in the brightness of stars, we can deduce the presence and characteristics of any planets that accompany them. Given the large number of existing galaxies and the large number of stars they contain, the search for these exoplanets or extrasolar planets is endless. What are the biosignatures (indicators of life) that will reveal the presence of life on distant exoplanets?