Buying security t-shirts to organize your event will do more good than you think. Most people think that security staff in an organization or even is only in charge of the security, but having a staff identified by a unified security t-shirts does more than keep an event safe.
Participants in any event need to know where to go for answers to basic questions or where to seek help in case of an emergency. Having your organization distinguished from the crowd will do a lot of good for any event.
Security members play many roles in any event, if you require your security team to stand out in the crowd, use bright yellow t-shirts with the word security printed on front & back with large black lettering. On the other hand, if you require your security staff to be faded in the background and only show up in case of an emergency, have them wear a black t-shirt with the word security printed with white ink across the back & front.