bitcoin sign & verify message

Blockchain.info

Step 1: Click on "Receive Money" Tab.
Step 2: Select your Address from which you want to Sign message and click on "Actions" button,
You will get a drop-down menu, Click on "Sign Message" Option.

Step 3: Type your message in "Message Box" and click on "Sign Message"
Final Step: It will generate a "Signature".
You need to give your Address, Message and signature and to prove your address ownership.


Electrum:

Step 1: Start Electrum Client and Click on "Receive" Tab.
Step 2: Right Click on the Address from which you want to Sign message and select "Sign message" in drop-down list.
Step 3: Type your message in "Message Box" and click on "Sign" Button.
Step 4: Enter your wallet password and click on "OK" button.
Final Step: It will generate a "Signature".
You need to give your Address, Message and signature and to prove your address ownership.

Bitcoin QT:

Step 1: Click on Receive Tab
Step 2: Right Click on the Address from which you want to Sign message and Select "Sign Message" in drop-down list.
Step 3: Type your message in "Message Box" and click on "Sign Message" Button.
Final Step: It will generate a "Signature".
You need to give your Address, Message and signature and to prove your address ownership.