This Pug just officially has a nice, double curled tail. As you can see it has one large curl and then the end of the tail swirls over once more and it is held tightly. Some double tails make two complete circles of the same length.
This swirly feature is not all that common and is considered to be highly desirable in all major kennel organization show rings. No worries if your Pug does not have a double curl, it's not overly prevalent. How many Pugs have two double curls? Approximately 25% of all registered purebreds. Two complete loops is the exception, not the norm.