If you want to buy personalized dog tag necklaces to wear as a civilian and you aren't familiar at all with the military, you should probably learn a bit about the history of dog tags AND dog tag necklaces.
Simply speaking, dog tags are a rectangular metal disc shaped tag engraved with a soldier's identifying information, e.g. name, social security number or service number, blood type and allergies, religion, and other pertinent information depending on the branch of service that they belong to. Dog tags (and necklaces with dog tags) come in a pair of two and serve a very practical service of identifying the soldier in case they are wounded or killed during battle. They (military medical personnel) will allow much quicker medical care for those soldiers who are injured and are identifiable with a dog tag and dog tag necklace.
Dog tags are required to be worn when a soldier is on active duty, is on an airplane, or is overseas. Dog tag necklaces must be worn around the neck at all times in those instances.
The custom dog tag necklaces consist of two tags with one tag on a 24" chain and the other tag being hung on the main chain with a 4" chain. This is done so that the tag on the 4" chain can be placed on a deceased soldier's toe if killed in the line of duty. The other tag can be taken off if the body needs to stay on the battleground for some reason.
If the soldier is not on active duty or in any of the other required situations, they can wear their dog tags (and dog tag necklaces) as they wish. It is considered in bad taste to wear the dog tags (and dog tag necklaces) visible in civilian clothes.
The military didn't always have dog tags (and modern-day dog tag necklaces). From the Civil War times and up through approximately 1906, soldiers were forced to find ways to manufacture their own identifying badges. There were some who would print their names and addresses on paper and pin it to the back of their coats. Others would try to etch it into the soft lead of their army pants' belt buckles. There were even some who made a close version of the dog tag (rudimentary dog tag necklaces) out of wood with a perforated hole for string to go around their neck.
Then in 1906, a circular aluminum disc was made, and in 1913 it was deemed mandatory that all soldiers wear their identification tags (the first iteration of dog tag necklaces). These circular tags were being hand stamped with name, rank, serial number, unit and religion; and were used throughout World War I.
When World War II came, the tags (on the dog tag necklaces) were replaced with a more oval-shaped tag, ushering in the second iteration of dog tag necklaces which is still being used through today. Because of the resemblance the tags had with dog collar tags, they developed the term ‘dog tags' to identify these 'dog tag necklaces'. They were no longer stamped by hand, but rather by machine; Silencers were added in 1944 so the tags wouldn't jingle together, and by the time of the Vietnam War, Social Security numbers were being added to the tags as the main form of ID.
The army is currently trying out new versions of dog tags with varying new labels from their current ‘dog tag', e.g. personal information carrier, meditag, individual carried record, soldier data tag. These new dog tags will offer a microchip or possibly a USB type of technology holding the soldier's dental information as well as other vital medical records.
Soldiers don't have a fondness for their dogs tags and don't like wearing them for what they represent. Dog tag necklaces sentimentally have no place in the fashion world as a means of strictly pushing ‘fashion' agendas. Gold dog tag necklaces should not be considered as just accessories to an outfit. Personalized dog tag necklaces shouldn't be visible to the public. They should be placed inside your shirt with either a silencer or a on a different level chain. That's the appropriate way to wear dog tags as necklaces.
There are reasons to have dog tag necklaces if you are a civilian. If you have a medical condition, this is a good way to have that information on you at all times, around your neck and visibly displayed. There are also people who have lost family members or loved ones in the military who have their dog tags and want to wear them in memory of them. There's also significant others who may want to get gold dog tag necklaces as a keepsake replication of their partner's dog tags to wear around their neck.
As long as there is a respectable reason to get and wear custom dog tag necklaces, and it is done in the proper way that they're supposed to be worn, there would be no sentimental harm to soldiers. We just always need to have respect for the men and women who are out there doing their best to keep us all safe and free. They are putting their lives up, and these tags keep them from being marked as unknown in active duty. They (the dog tag necklaces) bring them home. Isn't that a beautiful thing?