Sign up implies making an account with a trusted server. You don't *need* to sign up on memo.cash, you can just use your private key on any OP_return compatible wallet to make memos.
Fair enough. I have no idea when Memo support is coming to the likes of Electron Cash or anything like that.
memo.cash isn't the only way to read/write memo data. There are a few other clients, but the only wallet I'm aware of is the Telescope wallet, which is a browser extension
