Clear facts indicating that you have been abducted by aliens:

You can hear voices in your head. This can probably be the sign indicating that you were abducted by aliens, but before claiming that fact make sure you don't have earphones on.

You are sure that you saw an alien yesterday. It can probably be the sign that you were abducted. But make sure that yesterday wasn't Halloween and you weren't threatened by children of the neighborhood.

You have some superpowers. If you don't work in atomic power plant, then yes, probably you were abducted.

It feels like you had anal sex yesterday. It could be a clear sign that aliens have done some medical experiments with you (if you are heterosexual). But before claiming that you were abducted by aliens check if you are not involved in politics, religion, or professional wrestling.

If you recently encountered forces you could not understand, make sure that you were not communicating with religious leaders or Wall Street stock brokers. If you are convinced you were not, then it might be so that you had contact with alien life species.