For the past century, the primary symbol related to Ku Klux Klan groups (other than Klan robes themselves) is what Klan members may call the MIOAK (an acronym for "Mystic Insignia of a Klansman"). It is more commonly referred to as the "Blood Drop" Cross. It appears as a square white cross in black outline against a circular red background. In the middle of the cross is what appears to be a drop of red blood.
Though even most Klan group members don't know it, this symbol originated as neither a cross nor a blood drop. In the early 1900s, when the so-called "Second Ku Klux Klan" emerged, it adopted a symbol consisting of four letter "K" images arranged in a square facing outwards. In the center was a yin-yang symbol. In subsequent years, however, the four letters were re-oriented to a more vertical position, causing the symbol to look like a cross instead. At the same time, the white part of the yin-yang symbol disappeared, leaving only the colored part, which resembled a drop of blood. Thus eventually, many Klansmen came to believe that their symbol was a cross and that the "blood drop" represented blood shed to protect the white race.
Today there is no single "Ku Klux Klan." Rather, it is now simply a type of hate group and there are typically several dozen different active Klan groups around the United States at any given time.