Can nosebleeds be a sign of kidney cancer?

Not likely: Nose bleeds (epistaxis) can be caused by many things including picking (#1), vascular problems, blood problems. Kidney cancer would not be anywhere on my differential list of etiologies.

Most likely Not: Common things happen commonly. Nose bleeds most commonly are caused by trauma ( picking nose, blowing nose etc), dry weather/low humidity, blood vessels, deviated septum etc). Avoid trauma, humidifier, saline spray etc may help. While patient with cancer who are on chemotherapy or + extensive bone mets can have low platelet and that can be presented with nose bleed. That is stretching way too far.