Blood in your urine. I had bladder cancer, and the first indicator was blood in my urine, from the tumor being jostled or something and bleeding into my badder. My GP at the time assumed it was a bladder infection and treated me with antibiotics, despite any indication of an elevated white cell count. A year later I had a recurrence of the blood in my urine, and my much more competent new GP sent me to a urologist. The urologist found a tumor shaped like a cauliflower floret, about 3 cm across, attached to the dome of my bladder. After three surgeries and three rounds of chemotherapy, I have been cancer-free for over 10 years. I still have a cystoscopy at least once a year, and I am scheduled for surgery again for a biopsy next month, the fifth of those since my final resection to remove cancerous tissue. (A cystoscopy is where they stick a fiber-optic cable attached to a camera into your bladder through your urethra to look at the inside. My urologist has his fed to a 55-inch monitor on the examining room wall so at least I get to see what he sees. It is no fun, and urinating afterwards is excruciatingly painful for 3-5 days.) 80% of bladder cancer suffers are smokers; am not but both my parents were heavy smokers so mine may have been triggered by second-hand smoke. TL; DR: blood in your urine? See a urologist!