How do atheists show their beliefs?

Members of almost any group generally blend in with the "public" behavior of their culture. In the case of atheists we do not seek out Christians to disparage, kittens to bite the heads off, churches to burn, or carry a copy of Marcus Aurelius' work (Meditations) to give us talking points when we start spontaneous street corner meetings. The classic complaint is that atheists fume and sputter at a Xmas carol in a store or a clerk's failure to use the P.C. "Happy Holidays!". This is not the usual case any more than expecting Christians to become apoplectic at the sight of a burkha.

Considering that 10% to 30% of the populations of most European and North American cities are atheists, agnostics or other non-believers it is likely that you witness their public behavior daily - without it ever drawing any attention.