The most obvious sign of a leaking roof is a ceiling stain or drip that appears after rain. Other indicators include damp patches, bubbling paint, rust stains, or mould in upper corners. Drips from light fittings or fan hooks may also signal a leak. Before repairing, rule out other causes like plumbing leaks or condensation, which can mimic roof leaks. Identifying the true source is crucial for effective repairs.