Auspitz's sign is the appearance of punctate bleeding spots when psoriasis scales are scraped off, named after Heinrich Auspitz. This happens because there is thinning of the epidermal layer overlying the tips of the dermal papillae and blood vessels within the papillae are dilated and tortuous, which bleed readily when the scale is removed.
References
Auspitz's sign Wikipedia(Text) CC BY-SA