The symbol of the Deathly Hallows, in which the vertical line represents the elder wand, the circle represents the resurrection stone, and the triangle represents the invisibility cloak. The symbol of the Deathly Hallows was once thought to be the symbol of the famous black wizard Gellert greendevo. Voldemort's grandfather, marvoro Gunter, used to think of it as the pevrier coat of arms. There is a figure that looks like a triangular eye with a vertical line in the middle of the pupil.

"The elder wand." he drew a vertical line on parchment. "Resurrection stone." he added a circle to the vertical line. "Invisibility cloak" he drew a triangle outside the vertical line and circle, which became the symbol that fascinated Hermione so much. "Together is the Deathly Hallows."

Source: @hellion_tattoos