**Core Concept**
The Auspitz sign is a clinical finding associated with psoriasis, a chronic autoimmune skin condition characterized by thickened, scaly plaques. It is a key diagnostic feature that helps differentiate psoriasis from other dermatological conditions. The Auspitz sign is a result of the histopathological changes in the skin, particularly the thickening of the stratum corneum and the presence of Munro's microabscesses.

**Why the Correct Answer is Right**
The Auspitz sign is observed when scales are gently scraped off from a psoriatic plaque, revealing pinpoint bleeding points (punctate hemorrhages) due to the thinning of the epidermis and the presence of dilated capillaries at the dermo-epidermal junction. This phenomenon is a result of the abnormal keratinocyte proliferation and the subsequent increase in the length of the rete ridges. The bleeding points are a direct consequence of the rupture of these dilated capillaries.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the Auspitz sign is not typically associated with seborrheic dermatitis, which is a different skin condition characterized by a scaly, itchy, and inflamed appearance.
**Option B:** This option is incorrect because the Auspitz sign is not a feature of atopic dermatitis, which is a chronic inflammatory skin condition often associated with allergies and asthma.
**Option C:** This option is incorrect because the Auspitz sign is not seen in lichen planus, a chronic inflammatory skin condition characterized by a flat-topped, polygonal, purple rash.

**Clinical Pearl / High-Yield Fact**
The Auspitz sign is a classic clinical finding that can aid in the diagnosis of psoriasis. Remember that the presence of pinpoint bleeding points after gentle scaling of a skin lesion is highly suggestive of psoriasis.

**Correct Answer: C. Lichen planus**