This is a large cardboard standee made for Sonic Adventure DX. It also has a dot on it that apparently is announcing a free ringtone as a bonus of some sort. All of Sonic is there (though he is covered by items in this photo) and it is rather large, standing at least 4 feet high.

This originally was used to announce SA DX in HMV in Trocadero, Londons West End. Interestingly, that is the same site where Segaworld London used to be. Usually, when a store is finished with large cardboard items like this, they can be aquired by fans. (ie- when a game's promotion period is over)