Everyone deals with the issues of tags, collars and identification differently.
Some people attach the tags to the martingale and the greyhound wears a martingale all the time. I, personally, don't like this idea because I worry that the hound could get caught on something and hurt or choke themselves while no one is around. I particularly worry about this when a greyhound is crated. When we crate fosters when we leave, I remove their collar.
Some people just let their hounds run around naked when they don't need a martingale, such and in the house or in their fenced yard. I rarely let my hounds be "naked". It just makes me nervous for them to have no visible identification on.
Then there is the option we chose and recommend to those who ask. This is also a variation of the method many of people who I seek my advice from use.
First, there is the "around the house" collar. When a martingale is unnecessary, my greyhounds wear a plain dog collar. We currently use just plain buckle dog collars. I know other people who use the plastic clip kind. That doesn't reall matter. What matters is, it is a looser collar that the greyhound more easily could get out of is he or she got hung up on something. Yes, there is a chance that this collar would come off of your greyhound if they got out, but, they will not choke themselves.
Second, there is identification. Some people have gotten collars that have the dog's name and their phone number embroidered on the collar (if you want to know where to get one of these collars, post a comment or e-mail me). These work just fine. They also have tags as well. We have tags, but not the embroidered collars. Our greyhounds are also microchipped. Personally, I recommend it. If you dog ever does get out and loses it's collar, if it gets picked up, you always have a back-up.
Third, there is the martingale. Okay, so you have all your hound's identification on another collar, so what do you do when you need to use a martingale. There are a few options here. We used to leave the plain collar, with tags attached, on whenever we left the house. Our dogs wore both the plain collar and the martingale. This works just fine, but eventually we decided it looked funy for them to have 2 collars on. It really doesn't matter, as we know others who do this, but we chose to go another route. Instead of 2 collars, we put all our hound's tags on a single ket-ring and then we put that key-ring on a carabiner, though you could use any type of "clip" device you wanted. Then we move the tags from the plain collar to the martingale with ease. The carabiner also serves another purpose, as a back-up to the leash clip. We actually clip the leash and the d-ring on the carabiner so that if the clip let go for some reason, there was a back-up. We've never had a leash failure, but we have heard of a few people who have.
Below are some pictures to, hopefully, make sense of everything I talked about above.
Here is Anna in her "plain"collar with her tags on the carabiner. This lose collar is less of a choking hazard than a martingale when she if left home alone or in a crate.
Here is a close-up of Anna's tags on the carabiner.
Here is a martingale, leash, and tags on a carabiner.
This shows the carabiner attached to the collar, not at the d-ring. If you are not using a carabiner or are not attaching the carabiner back to the leash, this is the preferred location of the tags. If the tags got caught on something, they are less likely tobe a choking hazard for your dog if they are on one of the others rings, rather than the d-ring that pulls the martingale tighter.
This shows the carabiner, with tags, attached to the d-ring of the collar and back to the swivel part of the leash. If there was a problem with the clip on the leash, this carabiner acts as a back up.
So those are my thoughts, and images, on tags, collars and identification. I hope this information is helpful. If you have any questions or comments about anything I talked about or showed or where you can get anything I talk about or show in my pictures, just send me an e-mail or post a comment here.