To set up your e-mail signatures:
- Launch the Settings app and then select Mail, Contacts, Calendars.
- Scroll down until you find the Signature option and tap on it.
- You'll be presented with the option to set one e-mail address for all accounts, or to set a signature per account.
- Use the latter option to customize the signature for each account.
Now iOS will automatically apply the proper signature based on the account you're using to send the e-mail and your work account emails will no longer be guerrilla marketing for Apple.