Crowds quickly gathered to gawk at the lettuce lady, but police were not amused.
Officers briefly arrested the Jordanian activist, Amina Tarek, and a colleague from People for the Ethical Treatment of Animals.
The pair stood in a square along one of Amman's trendiest streets and held a placard reading "Let vegetarianism grow on you."
Tarek says she wanted Jordanians "to turn over a new leaf."
Police held them for three hours, saying they had not obtained permission for Sunday's protest. The activists say they had approval.