Do be aware of a condition called pyometra in un-spayed bitches, which is an infection of the uterus and can present as signs of coming into season. The discharge is, however, slightly more watery and eventually quite smelly, but they DO attract dogs because of their hormonal confusion !
This needs immediate Veterinary attention and unless detected very early, normally needs a hysterectomy to return the dog to full health.
My Lab that I had before I got Barley the Cocker had this, and we were lucky to save her, as she had been due in season, and I just thought that was what it was .. Luckily my Vet is ace and turned out on a Saturday night (with her Nurse), operated, sat up all night watching Poppy to make sure she was okay, walked her out in the morning, and returned a grateful and healthy dog to me !!