You get the Help4Pets tags when you subscribe to the Rover Protection Program. It includes a year long subscription to the service.
For Rover, the tags are registered to a sitter, so if a dog gets loose during a stay, anyone who finds them will be put in touch with their sitter (and Rover) rather than with the owner, who is presumably out of town and unable to come claim their dog. It's an added layer of protection, even if the dog is wearing tags or has a microchip, since there is a good chance the sitter will be easier to contact and more available.
Oops. I think I somehow down-rated your question by accident. I apologize - it's been voted back up again.