Coinomi allows you to sign and verify messages on all supported coins. By signing a message with your address, you can prove that you own that address without the need to send any coins from it.
- Open the wallet of the coin you want to use for signing
- On the "receive" screen, copy the address you want to sign with
- Back to the "balance" screen, select "... - Sign/veirfy message"
- Paste the address you want to sign on the first box
- Write the address you want to sign. If participating on any airdrop or contest that requires it, make sure that the message is exactly the one they ask you to sign. A single extra character, or even replacing a lowercase letter for an uppercase one generates a signature different from the expected.
- Press the "sign" button and confirm your password
- Copy the signature completely, and share it along with the address and message to anyone, as proof that you control that address.
- Open a wallet of the coin that was used to sign a message
- Paste the address that was used to sign on the first box
- Paste the message that was signed on the second box
- Paste the signature on the third box
- Press the "verify" button.
- You will see a note saying "Message verified" if the signature matches the address, thus proving that whoever signed the message controls that address. Otherwise you will see a note saying "Message verification failed"
Signing with coins of the Ethereum family
Except for Ethereum, other coins of the Ethereum family can't yet be used to sign/verify from within the app. You can use MyEtherWallet for that. Open the website https://vintage.myetherwallet.com/signmsg.html, follow these instructions to link your address to the MEW website, and sign the message there.