The notoriety level works very similarly to the Grand Theft Auto, Saints Row, and Just Cause series.
One Star: The Militia will slowly start tracking you down.
Two Stars: The Militia will start using lethal force on you.
Three Stars: Militia will work with the Securitate and use lethal force against you.
Four Stars: The military starts to get involved. Helicopters with armed snipers will come for you, including APC's with soldiers armed with Romanian AK-47s will try to subdue you.
Five Stars: This is better known as the "last resort". The Militia, Securitate, and the military will hunt you down on site. At this level, it will be complicated to evade, even though it's possible.