Why is it that some canon 600D have "rebel T3i" written on it?

i am seriously looking into buying the new canon D600 but when i go online, some of them have Rebel T3i written on it where some just have 600D written on it... i know the 600D is the successor to the 550D witch is the Rebel T2i and that the 600D is the rebel T3i but i just want to know why they write it on some and not others...