We hope that you have already read our tutorial on How to Add a cPanel email account to your Android Mobile, and you have already added a built-in email widget to your Android screen.
The built-in Android email application allows us to set a custom email signature, which will display at the end of your email.
1. Open the Email inbox icon.
2. In the top left, tap on Menu and then on the Settings option.
3. Select your email account. If you have multiple accounts, you can set different signatures for each account.
4. Tap on Mobile Signature. 
5.Set your customized signature and then tap on OK. 
Now, whenever you send an email or reply to one, the signature will be automatically added at the end of your email.