The symbol is a very curious thing. It pops up all over the place it appears not just the sword and on Jessica.
Here's a list from Google:
The symbol appears most frequently throughout the series. In episode 12 (Godsend), the symbol is revealed by Ando Masahashi to be a combination of two Japanese characters: ? (sai) meaning "great talent" and ? (yo) meaning "Godsend". It also greatly resembles a segment of RNA, connecting it to the genetic mutation giving the heroes their powers. Appearances include:
* As a decorative object in the Bennets' home
* In a swimming pool at the scene of one of Sylar's murders. Several flotation devices form the shape.
* On a billboard behind Hiro in Times Square when he teleports there.
* Frequently on a computer screen, scrolling across a genetic profiling program created by Chandra Suresh.
* On a drawing done by Peter Petrelli.
* On various paintings by Isaac Mendez.
* On a post-it note on the map in Mohinder Suresh's apartment.
* Written on a geometry textbook owned by Claire Bennet.
* Written on pictures in Sylar's apartment.
* On Jessica's back whenever she surfaces as Niki's alternate personality. Whether the symbol is also present on Niki's back is unknown.
* On the hilt of a katana once owned by 16th-century samurai Takezo Kensei, possibly the earliest known manifestation of the symbol. This katana is held by future Hiro and sought by present Hiro. The symbol also appears on the replica of the sword, which was stolen from the museum by Hiro.
* Printed on the front of Chandra Suresh's book, Activating Evolution.
* Printed on the upper-left corner of the 14th issue of 9th Wonders! comic book, written by Isaac Mendez.
* On a necklace worn by the Haitian.
* On a picture of Niki as "Jessica", painted by Isaac. The symbol was hidden under an extra layer of paint.
* Drawn on a Greyhound bus sign, seen right before D.L. spots the runaway Micah in the episode Homecoming.