When seenu admits shankar in hospital, he removes his personal items watch, chain with military style identification tags(aka dog tags) and gives them for placing as Shankars belongings. This is done so that police will believe Shankar as Seenu and will take him to custody.
From the next scene itself, we see a chain with id tags again in Seenu's neck. How is that possible? Even if we assume he bought a new chain with a id tag, it does not make sense as he is trying to pretend as he is Shankar and he is hiding his other activities like drinking from others.