As a Memphis native and current resident, I know that the Hernando de Soto Bridge has NEVER been called the "M Bridge" by a majority of locals. We call it one of four things, either the Hernando de Soto Bridge, the Memphis Bridge, the New Bridge, or the Mississippi Bridge. The name the Hernando-DeSoto being its official name, the name the Memphis Bridge coming from the fact that it connects West Memphis, Arkansas to Memphis, Tennessee, the name the New Bridge coming from the fact that the bridge is the newest bridge and is newer than the Old Bridge, or the I-55 Bridge, and lastly the name Mississippi Bridge comes from the fact that it crosses over the Mississippi River. Again, never in my life, except for seeing it on Wikipedia, have I ever heard the bridge called the "M Bridge."