Is blood on toilet paper after a bowel movement a common sign of colon cancer?

Not necessarily. Red blood on the toilet is not uncommon occasionally and can be caused by things such as a tiny anal erosion or fissure(especially with constipation) it can also be from a hemorrhoid. Blood mixed with stool or dark stool can be from bleeding farther inside the colon and should be investigated. Screening colonoscopy is recommended once you've reached 50 even with no symptoms.
Not necessarily. The most common causes of blood in the toilet paper are perhaps hemorrhoidal bleeding or bleeding from anal fissure. That does not mean that other causes like anal cancer/rectal cancer can't give that presentation. So, see your doctor and discuss further with your doctor. Further evaluation will need to be done- including direct examination, GI work-up like colonsocopy etc as indicated.
Not necessarily. Blood in stool is a possible sign of colon cancer, but blood on toilet paper may be part of hemorrhoids (or if female, vaginal bleeding). Polyps and inflammatory bowel disease can also cause blood in the stool. Colonoscopy with guiac stool testing can help to sort this out.
Hemorrhoid more like. Bright blood on toilet paper is more likely to be due to hemorrhoids than colon cancer. However, even hemorrhoids can cause anemia and related health problems. Bleeding from any orifice is a good reason to consult your doctor.