[Quadraphinic]

My last Yorkie Megan had a heart condition, that kept her from getting spayed until she was 12, she had a major bladder infection that required emergency surgery, at which time she was spayed as well. That was four years ago, and I really never knew when she went in to heat. My question is, with a normal healthy Yorkie puppy, around 6 months old, what are the signs that she is going into heat? I want to get her spayed in November, but I think she might be starting her cycle. Thanks in advanced for any help and answers.
Cheers Quad