Email signatures are a standard part of a professional email. To create an email signature for the emails you send from Fleep, open up your Account menu and choose Email settings from the popup that appears.
There, you will see a section for your email signature:
You can add the signature from your Email settings. Just click on your profile in the desktop version, and choose Email settings from the menu that appears.
Fill in any fun (or professional... totally up to you!) signature message you like. And hit save!