That technique doesnt require any handseals, hence anyone can tell that clone is a fake/illusionary one.
Upon hearing the opponent's question, Obito raised his head. That was a sign to tell the foe that question was ridiculous in his part. Obito raised his right hand and put it in front of his spiral mask, muttering something. You really think a non existent person, is allowed to have a name? Obito stood there silently, loweing his hand and waiting for the opponent's reaction, which was creating a clone. The fact he didn't use any handseals, it was easy for Obito to tell it was an illusionary clone, mainly used for distractions. Obito grabbed a chain which was hidden in his right arm. He then locked his right wrist with the chain, this way he would have it easier to controll it. Slightly swinging his arm in a wave motion, in order to send the chain near the opponent. The chain would move in a circular formation and trap the opponent around his hip, restricting his movement. Then with his left arm, Obito would throws a single kunai aimed at the opponent's throat.