If the religious stop making public statements, so will atheists. If atheists shut up, the religious will continue to evangelize. The FFRF wants there to be less religion in public spaces (the thing you want) but instead of a sign saying "there shouldn't be a manger or menorah here" or "Dear Religious People, please shut up" they made this statement instead.

If you're going to beg anyone to shut up, go to a church. The people who made this sign are on your side.