Magician disappears a signed coin and  takes out a very tightly locked transparent box. 

That missing and signed coin appears in the box. 

The magician passes the box to the audience and lets him take the coin out, but the audience can not open by any way. 

Finally the magician, with lightning speed, opens the box! she pours out the signed coin, and then takes the lid back to the box. 

The audience gets the box again, but he still can not open it.

It is a fun close-up trick.