Signing text to prove that it was written by an orchard ZEC address-holder.
Bitcoin and many other currencies support this.
It’s how “Connect Wallet” works on Ethereum, NEAR, and other currencies for logging into a website using your wallet. (see Uniswap, ENS, NEAR Intents, etc.)
We need to define the standard for how to do this. I believe it’s a very quick win and essential for Zcash wallets to be useful for authentication on web apps.
An example from Bitcoin:
-----BEGIN BITCOIN SIGNED MESSAGE-----
Hello Zcash world from Bitcoin testnet4!
-----BEGIN BITCOIN SIGNATURE-----
IEehKzHRPN5lBEWY2PJtCbkmel6uNSxi4nj0h2SOqd6sbWqrdFFb0VDuzusYbkuRVhXbyCIrpszYwzcb92eNaZY=
tb1qvepl70wg73tepyspckn7gdgg533y9jpex93xc2
-----END BITCOIN SIGNATURE-----