Thanks Saschia, this is what we are hoping to do and thanks for your good wishes
. Saying there is a tattoo, but not what it is will stop the wrong people claiming the dog. I was surprised to be told she had a tattoo on her ear as I thought it was only dogs whose ears are not erect had it there too. Unfortunately, I have not been able to find out the microchip number (if there is one...). Even if she is a mutt, by all accounts she is a lovely dog and must surely be missed by her owners. She deserves all we can do to get her home.
My vet gave me the name of a Bulgarian site that I hope to place an ad on later.