It seems like there are two common ways to lose coins:

1.  wallet is stolen
2.  there is a fork in the block chain, or major systematic problems with the whole coin system

next, it seems there are two ways to store coins

1.  in your local wallet
2.  on a major exchange website.

If we combine those two sets of choices, there are a few combinations.    For each of those combinations,  how do you find out that your coins are "gone"?    how will you know.       for example, would your wallet suddenly show "empty".   or you wouldn't know they are gone, until you tried to spend the coins.

thanks.

-newbie