Looked at the whole video and I do not know New York law. I does the sidewalk around the building belong to Trump or is it owned by the city?
The sign was clearly blocking access from the street and the sign was too big for someone to be carrying (a moving protest). If it was stationary on Trump”s property he may have had a right to remove it. I am not a lawyer.
Public Sidewalks are the property of the City.
I’ll link you to a place where I addressed this earlier. It’s my best thoughts on it.
http://www.freerepublic.com/focus/news/3332862/posts?page=125#125
It wasn’t removed, it was walked through like a finish line of a race.