The autograph of a sumotori
Tegata literally means Shape of the Hand, and a tegata is a handprint made with ink on a piece of shikishi paper. It has been the traditional autograph of the sumo wrestler, but as other sports have gained influence and popularity in Japan the tegata are no longer exclusively sumo related, but made by many sportsmen, eg. baseball and soccer players.
Until the 70s the colour of the ink was almost always black, but since then the predominant colour has been a red/orange (shu-iro). Beside or across the imprint of the hand the wrestler will write or paint his name with black ink.
A tegata will often sport the seal of the wrestler's heya (training school or 'stable'). Every heya has its own unique seal, and it is stamped onto the tegata as proof of authenticity. Tegata are very collectable, and especially the stamped ones are popular.
There are some good pictures of tegata here
This is, as always, a great source of information: http://www.sumoforum.net/glossary.html