Taraneh Alidoosti's tattoo was seen sneaking from under her sleeve this week as she addressed reporters after returning from the Cannes Film Festival, where her latest film "The Salesman" won two awards.
The images sparked intrigue and intense debate on Iran's colourful social media scene.
Some media claimed the pictures were fake while some online commentators accused her of advocating feminism - which is viewed negatively among hardline conservatives in Iran.
Alidoosti, 32, explained on Twitter the meaning of the "Feminist Fist" symbol, reminding fans in another update that she had previously explained that she viewed feminism as being about "showing unity and fairness".
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"Keep calm and YES I'm a feminist," she said in a series of tweets on Tuesday night. "Feminist: a person who believes in the social, political, and economical equality of the sexes."
One follower @RaminRamroodi replied "Keep calm and You will be in Evin Prison Tomorrow" - referencing the notorious Tehran jail - to which Alidoosti replied with several smiley faces.
Several famous football players have been summoned to Iran's sports morality committee for showing their tattoos.
Alidoosti's Instagram is one of the most popular Iranian accounts on the photo-sharing app, with 2.6 million followers.
Last year she responded to a spam message for vacuum cleaners that said the products were "only for women".
"Those who think of a vacuum cleaner as designed only for women... Insult not only women but all the men... Who don't see their own kind as their waitresses," she posted on her account.
In a rare move, Iranian media published pictures of her different outfits at Cannes, drawing tens of thousands of responses from social media users weighing in on beauty, fashion and adherence to Islamic dress codes for women.
Alidoosti is married and has a young daughter.