The conceptual "Thin Blue Line" is derived from the historical Thin Red Line.
Proponents of the symbol assert that the identifier is intended to show support for police.
The Blue line stands for the Law Enforcement Officers. The top black part stands for The good. And the bottom black part stands for the bad. All together, the Blue Line (Law Enforcement) separating the good from the bad.
Opponents claim that display of Thin Blue Line emblems is used to gain favorable treatment from officers (colloquially referred to in the United States as "flashing tin", meaning presenting a badge) in order to get immunity from traffic tickets (also known as "professional courtesy").  Even serious offences such as drunk driving are subject to professional courtesy "discretion", and federal law assists in the process by exempting police officers and firefighters from a federal law that requires truckers to be blood-tested after an accident.
The ability to break traffic laws with impunity has led some non-police to use thin blue line bumper stickers. Some purveyors have responded by restricting their sale to people giving their department phone number and badge number, e.g.
Thin Blue Line Decal
This is a Law Enforcement Restricted Item
We require proof of your status as LE before processing your order. You must provide a faxed photocopy
or scanned email copy of your current department I.D. for verification.
This has the effect of either preventing non police from showing their support of police or preventing non-police from getting out of traffic tickets, depending on which theory one believes.
Police have attempted to prevent non-police from using such stickers in order to support the police / get out of tickets by supporting laws that stop anyone but a LEO from displaying such stickers, but these laws have been struck down.  
The design is now commonly acknowledged as part of the public domain. See Genericized trademark for explanation of Public Domain in this case.
After the popularity of the Thin Blue Line emblem for law enforcement came a number of other "thin lines".
- Thin Orange Line — Bounty Hunters
- Thin Red Line — Firefighters,
- Thin Silver Line — Corrections officers
- Thin Yellow Line — Security Officers, Retail Loss Prevention
- Thin Green Line — Federal Agents, especially Border Patrol Agents, and park rangers
- Thin NWU Line — United States Navy
- Thin ACU Line — United States Army
- Thin Tiger Stripe Line — Air Force
- Thin White Line — Emergency medical services. The thin white line differs from other thin lines in that the background is blue instead of black, with a white line crossing horizontally through the middle.
- Thin Blue Line with Lightning Bolt — S.W.A.T. (Special Weapons And Tactics)
The Gold Star attribute signifies law enforcement and military officers who have retired or are currently serving meritoriously.
- ↑ Special license plates shield officials from traffic tickets. ocregister.com. Retrieved on 2009-06-02.
- ↑ Nalder, Eric; Kamb, Lewis; Investigative, P-I (2007-08-05). "A broken system works in favor of cops busted for DUI". seattlepi.com. http://www.seattlepi.com/specials/undueinfluence/326446_dui06.html. Retrieved 2009-06-02.
- ↑ http://www.wired.com/threatlevel/2010/04/police-bumper-stickers/
- ↑ http://www.firstamendmentcenter.org/village-cant-bar-civilians-from-displaying-police-related-decals
| This article uses material from the Wikipedia article The Thin Blue Line (emblem), that was deleted or is being discussed for deletion, which is released under the Creative Commons Attribution-ShareAlike 3.0 Unported License.