Answer: Endocrine
A chemical signal produced in the pituitary gland at the base of the brain binds to a receptor on liver cells. This signal would be classified as an endocrine signal.
Step-by-step explanation:
An endocrine signal is produced by a cell that targets a distant cell through the bloodstream.
Hence, a endocrine signal (carried by hormones) produced at the base of the brain (usually an endocrine gland) travels through the bloodstream to the target cell and binds to a receptor on the liver, and then exerts its function.