Shows that the iPhone screen is locked in portrait orientation. See “Viewing in portrait or landscape orientation” on page 21 of iPhone User Guide (For iOS 5.1 Software)
Lock the screen in portrait orientation: Double-click the Home button , flick the bottom of the
screen from left to right, then tap Right circle arrow.
Get your User Guide on your iPhone. Goto your App Store icon in your iPhone. Search for "iBooks" free download from Apple. Open iBooks. Tap on "Store" in top right corner. Search for iPhone user guide for IOS 5.1. Open user guide and search for Portrait Orientation Lock.