who says i have any bitcoin? i just believe in the cause of fair money.
Be careful with this, remember the Feds took down the mob by proving tax evasion, not actual crimes.
If the US government (with all of the data collected by NSA, etc) is able to prove that at one point you acquired a certain number of coins then it is easy for them to force to you admit to one of the following, either:
1) You sold the coins, in which case you better have reported that past sale to the IRS and paid taxes, or
2) You still control the coins
Anonymizing your coins doesn't help, either you sold them or you have them.
A windfall profits tax can easily be enabled by creating a tax event. For example let's say the government decides to eventually recognize bitcoin as money and no longer property, that event could be interpreted as a tax event forcing taxes on all unrealized gains from converting "property" into money. This isn't far fetched, EVERYTHING is interpreted/justified through the tax code today.
I think it's wise to either:
1) Be like Satoshi and ensure you are 100% hidden, or
2) Be completely transparent and honest with the government in your bitcoin dealings, including public posts, because it all will be used against you. I am following 2. It's a free bitcoin world so feel free to do what makes sense for you.