Are cryptocurrency logos copyrighted?

Each unique cryptocurrency logo will have its own answer to this question. But here are some examples: The original unaltered bitcoin logo is free of copyright. There are also many variants of the original that are also free. Other related alt-coins based on bitcoin may have copyrighted their own version of the original logo. And in fact, anyone can copyright their own altered version of the original bitcoin logo if it is sufficiently different from that original. Other cryptocurrencies do have specific guidelines, such as Ripple’s logo usage guidelines here.  The Ethereum logo usage guidelines can be found here.
For any other cryptocurrency logos, you will have to do your own digging.