1. Unexplained Weight Loss: If you lose more than 5 kilograms in a month without dieting or exercising, it could indicate cancer, especially stomach, lung, or pancreatic cancer. 

2. Persistent Fatigue: Feeling constantly tired without reason may be a sign of cancer, like leukemia, lymphoma, or liver cancer. 

3. Unexplained Bleeding or Discharge: Coughing up blood, rectal bleeding, blood in urine, or nipple discharge without any known cause might be cancer-related, particularly in lung, colon, bladder, or breast cancers.

4. Unexplained Lump or Mass: Any unexplained lump or mass in the breast, testicles, armpit, or neck, that does not diminish or change with menstrual cycles, could signify cancer, such as breast cancer, testicular cancer, lymphoma, or thyroid cancer.

5. Unexplained Pain: If you experience persistent or intermittent pain without any clear cause, like headaches, chest pain, abdominal pain, or bone pain, and standard pain relief methods are ineffective, it may be due to cancer, commonly brain, lung, pancreatic, or bone cancer.

6. Unexplained Skin or Mucous Membrane Changes: Noticeable changes in the skin or mucous membranes that don't heal or disappear, like pigmentation, ulcers, or blisters could be a sign of cancer, such as melanoma, oral cancer, or cervical cancer.