Why do football managers have their initials on their kit?

Answer 1

Most clubs have some sort of system that helps the kitman keep the laundry sorted. If you ever see pics of players in training they all have a 'kit number' - not always the same as their squad number [which appears on the back of their shirt].

For technical staff [manager, coaches, physios, etc] most clubs use initials. This way the right clothes end up back with their owners when the laundry is done.