Most agencies have a basic rank, usually called Police Officer, Deputy Sheriff, or Trooper, depending on the nature of the agency. Some may have grades within the basic rank, such as senior or master officer (deputy, trooper, etc), lead officer, senior lead officer, etc. At LAPD, there are Police Officer (PO) I, II, and III ranks. Probationary officers are PO Is, who move to PO II when they pass their probationary period. Police Officer IIIs wear two chevrons, similar to corporal stripes in the military. They may be training officers or other specialized positions. A Police Officer III + 1 has the two chevrons and a star, and is called a Senior Lead Officer. They serve as training officers and some area coordinators.
First line supervisors are usually sergeants, wearing three chevrons. Some agencies also have multiple levels of sergeant, like staff sergeant or master sergeant. In the photo below, the officer on the left is a senior lead officer (PO III + 1); the one on the right is a sergeant.
