On one side Surname, address including post code, and on the other side, both telephone numbers and I am Microchipped. I was a bit cross when I went to get Rufus's new matching blue tag for his Christmas present ( a blue Rogz collar and lead kept clean and smart for agility) because the shop was told by the manufacturer of the engraving machine to advise 3 lines, not 4 as I have always had, because they say the writing gets too small. The puppy foundation class tutor told us what to put. Apparently a trend had emerged of just putting house number, post code and "I am microchipped". However, some wardens and the police do not have immediate access to a scanner, and interpret the relevant provisions as requiring the address. She suggested both telephone numbers, because the chances are the dog is found while you are still out. I am pleased that Rufus, although very poor at recall when younger, was never lost. My friend however had to wait over night to trace her dog because there was no access to a scanner that day and no answer on the home phone while she was out. The person who found her dog called the warden, who had no space. This meant her dog got transferred and she had to pay the fee on recovery