The Microsoft account email ID is displayed by default in the login screen. To improve your privacy and security, you can hide your MSA email address from the login screen. Here is how to do that in Windows 10 v1607 (Anniversary Update).
Remove Email Address from Windows 10 Login Screen
Open Settings (WinKey + i), click Accounts, Sign-in Options.
Under Privacy, turn off the setting “Show account details (e.g. email address) on sign-in screen.”