Does the world really need to know that every email you write was "Sent from my HTC One™ X, an AT&T 4G LTE smartphone"? Probably not. Aside from turning you into a free marketing tool, it will give your friends fodder to tease you over your your choice of handset or carrier. Plus, it makes you look like a noob that doesn't have control over their email. These annoying signatures are easy to change, though, if you know where to look.
Changing the signature in iOS's Mail app
On iOS, go to the Settings app, tap Mail, Contacts Calendars, scroll down, then tap Signature. Once there, you can change your email signature, and choose whether you want a different signature for every email account you have (tap Per Account) or One Signature to Rule Them All (All Accounts). In my case, I modified the stock iPhone email signature to serve as a warning about the inevitable typos.
You can use your email signature yo warn your friends of wayward fingers.
Once you're done, tap the back button or close out of the Settings app.
On Android
Android typically comes with two mail apps: a general email app that will work with lots of different mail services (aptly named "Email") and one for Google's own Gmail service. The two apps are very similar to one another, and the process of changing your email signature is the same for both apps.
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