I have been selling my bitcoins earned from signature campaigns for more than a year now and never faced any problems with it. I sell them to local merchants in Localbitcoins.com and get the funds in my desired bank account and then i cash them out on ATM. There are no regulations regarding Bitcoin in my country and maybe that is the reason why i was never bothered by the bank or any authorities, but someone might have to answer a few questions if there are regulations implemented on Bitcoin in their country.
In my country too, the bank never questioned where our money came from. Maybe if someday, bitcoin really put in the list of taxpayers by the government, then we automatically have been taxed for it, for every transaction