Was the banner being used to impede the right of way onto Trump’s property? If so, then security had every right to remove it.
First, the banner was on the public sidewalk, at least 10-15 feet from the entrance to the building.
Second, regardless of where it was, Trump’s goon had no right to rip it from the guy’s hands. If they’re impeding access (which they weren’t), then instruct them to move. If they don’t move, then ask the police to move them or arrest them. Don’t assault them and take their property.