Poison Tattoo

Source Advanced Race Guide

This henna-like paste creates a dark brown tattoo on the hands or feet that fades over the next 2d6 days. The tattoo temporarily boosts the strength of a vishkanya’s natural poison, increasing the DC of the next weapon envenomed with the vishkanya’s blood or saliva by +2 (once used, the tattoo is merely decorative and does not affect the creature’s poison). A typical tattoo consists of intricate whorls and spiritual symbols on the hands or feet.