An unofficial vote is known as a straw poll. Most straw polls are conducted to get a general sense of people's opinion on an issue or political candidate.
Though straw polls are informal, they are somewhat structured, with specific polling times and restrictions against voting twice, for example. Because most are conducted among homogenous groups, they're less scientific than the random sample obtained in other opinion polls. Still, they are considered useful for reading the priorities of a political party or caucus. Some experts suspect the origin of straw poll comes from the idea of holding a piece of straw to see which way the wind is blowing.