picketer

/ˈpɪkɪtər/
noun
  1. A person who takes part in a protest or strike by standing or walking near a workplace or building, often carrying signs.
    • The picketers stood outside the store, asking customers not to shop there.
    • The company tried to negotiate with the picketers to end the strike.
    • Each picketer carried a sign that read 'Fair wages now!'