AK,
All targets are two dimensional and have both a ferrous and a conductive component. But, the tone is only one dimensional. The tone will only give you either the ferrous or conductive component depending upon the mode you select.
If you are using the CONDUCTIVE mode, then nails and silver sound about the same with silver being slightly lower pitched. Even thought the tones sound the same, the cursor position will be greatly different for the nail as compared to the silver coin. Therefore, you should check the cursor position (or the digital readout) before digging a nail. But for deeper silver the cursor tends to move to the left on the screen. If there is a nail and silver co-located, then the challenge becomes even greater.
If you are using the FERROUS mode, then it is very easy to tell the difference between a nail and a silver coin so long as you do not have both in the same hole.
Hope this helps,
Glenn