Start by carefully pouring just a drop of the bleach onto the item in question. If it is really made of silver, then the coin or jewelry will tarnish and quickly turn black.
Test with a magnet. In particular, use a strong magnet, such as the rare-earth magnet made out of neodymium. Silver is paramagnetic and exhibits only weak magnetic effects. If your magnet sticks strongly to the piece, it has a ferromagnetic core and is not silver.
