I think the only cryptocurrency that matters a lot at the moment is bitcoin.  I can't imagine any alliance of cryptocurrencies with a common logo until some other crypto beyond bitcoin gets somewhat important.  At the moment BTC has a little press and coverage, others are just hiding in the shadows so what would bitcoin gain by associating publically with them.  Already a lot of people think that bitcoin is just for pirates and weirdos, I want to make bitcoin more mainstreamly accepted not to pull it towards weirdo land.