Getting Stopped by Police
We were stopped at many military police roadblocks while traveling. An expatriot american friend of mine gave us the following advice which works all too well.
In your cars paperwork which you hand to the police, simply place 20R$. If the police decide to take it while looking over your papers, no problem. You didn't offer it and it helps to avoid potential issues. It's not a bribe.. rather an incentive and is a part of the brazilian way of life.
There are two kinds of police in Brazil, State and military. The state cops can be distinguished in Natal by the word ROCAM on their uniform. They generally travel in twos in buggy or by motorcycle. The military police are easy to spot, with high powered weapons at the ready and more of a military look about them.
All police in Brazil generally will not bother you too much if you are a tourist as they know you have no need to pay the Brazilian fines or tickets they might impose on you.
Of the four times we were stopped at military roadblocks, none of the police took our money from the documentation. However, these were road blocks. If you get stopped for speeding or some other driving defense, the 20R$ is a good way to avoid potential problems and/or tickets while on an otherwise nice vacation.