I'm going to be a gatekeeper of a row at a sporting event
Why do you want to do that?  Do you work at the stadium?
No.  I just want to look important in front of other people.
You should not be a gatekeeper if you do not own the property or are not hired to do something about it. People might get very upset if they think that you are messing with them, and they have a right to enjoy the event that they paid for.
I'm going to wear a siren to signify that I'm a gatekeeper of this row.
Unless you are just joking around with me, I have to reiterate that you should not try to block people from accessing the seats that they paid for.  This is not your job, your responsibility, or your right as a ticket holder.  You are free to guard your own property, but not anyone else's.