**Core Concept**
Upper motor neuron (UMN) lesions occur due to damage to the motor pathways in the central nervous system, including the cerebral cortex, spinal cord, and brainstem. This damage disrupts the normal flow of nerve impulses, leading to various motor symptoms.

**Why the Correct Answer is Right**
A UMN lesion typically presents with spasticity, which is an increase in muscle tone leading to stiffness and rigidity. This is due to the loss of inhibitory influences from the cerebral cortex on the spinal cord's reflex centers. The Babinski sign, characterized by extension of the great toe and fanning of the other toes, is a classical sign of UMN lesions. Hyperreflexia, or increased deep tendon reflexes, is also a common feature of UMN lesions. The presence of weakness is more characteristic of lower motor neuron (LMN) lesions.

**Why Each Wrong Option is Incorrect**
**Option A:** Rigidity is more characteristic of Parkinson's disease, which is a lower motor neuron disorder.
**Option B:** Rigidity is not a typical feature of UMN lesions.
**Option D:** Weakness is more characteristic of LMN lesions.

**Clinical Pearl / High-Yield Fact**
Remember that UMN lesions typically present with spasticity, hyperreflexia, and the Babinski sign, while LMN lesions are characterized by weakness, atrophy, and decreased reflexes.

**Correct Answer: C. Babinski sign**