If you have aliases configured in Gmail, you can use them to send and receive email in Propeller. Aliases are configured in your Gmail settings here:
If you make changes to these settings after setting up Propeller, you can update by going to your settings page and clicking Refresh.
If your imported signature doesn't look right for any reason, you can modify it for just for use in Propeller using the editor.
When you send email from within Propeller, you can choose which alias to use.