I'm trying to find an easy way to scan the blockchain for contracts that support a particular ABI. Take ERC20 as an example: What is the easiest way to find all the ERC20 supporting contracts on the public Ethereum blockchain?

I know I need to search for the function signatures from the ABI in the blockchain contract bytecode. Is there any way to do this without writing some custom code and if it requires custom code, are there any examples available?

I'm using Geth currently to run my node.