Canary Mail allows you to include a custom signature with each outgoing message on your Android devices. 1. Open the application. 2. At the upper-left corner of the screen, tap the Hamburger icon. 3. In the upper-right corner of the screen, tap the Settings icon. 4. Scroll to the composing section. 5. Tap Signatures. 6. Enter a plain-text signature. (HTML is not supported at this time) You can also enter signatures per account.