[P-Marlowe]

I see the Mexican assaulting the guard.

Why was the guard walking away with his sign?

[Georgia Girl 2]

When you are an agitator life can be chitty oh and unfair. :-)

[Heart-Rest]

"Why was the guard walking away with his sign?"

At this point none of us know, because the video doesn't show what immediately preceded this action, and none of us witnessed it.

Just to give you one alternative possibility to think about, take a look at this brief video clip of an "Occupy LA" protest, showing at one point a protester physically attacking police officers with protest signs, which can be used as weapons when there are boards (or fists) behind the protest signs.   (If a person is physically attacked by a person with a sign like that, they are, of course, permitted to defend themselves, and to remove the weapon used to attack them from the hands of the perpetrators.)

Check out this clip:    "Los Angeles Police attacked by two occupy LA - one officer taken to a hospital"