It might be her darting eyes or his heavy breathing. It could be the perspiration marks on the young man's sweatshirt, or the fidgety way she carries herself when she walks alone.
Come Super Bowl Sunday, officers on the perimeter of Raymond James Stadium will be employing Transportation Security Administration tactics of "behavior detection" to try to weed out and confront people whose physical characteristics indicate a person might be about to commit a crime.
About 70 officers from Tampa Police and Hillsborough County Sheriff's Office received eight hours of behavior detection training from TSA in preparation for Super Bowl XLIII, said Super Bowl Incident Commander and Tampa police Major John Bennett.
It is the first time TSA behavior detection officers, who will be working with the local agencies, has used the strategy during a Super Bowl, TSA Federal Security Director Gary Milano said.
"We are essentially adding another (security) layer that hasn't been done before," said Bennett, who traveled to Miami and Phoenix in preparation for Tampa's turn as host.
Bennett said he got the idea for strengthening security in the "grey area" just outside the stadium after an incident at Super Bowl XLII in Phoenix. In that case, a man angry about being denied a liquor license sent a manifesto to media, then drove within sight of the stadium with an assault rifle and 200 rounds of ammunition.
In applying the TSA methods, uniformed officers who notice odd behavior might engage individuals who catch their attention in conversation and ask a few questions. The questions might lead to more questions - and, if suspicions persist, possible interrogation and arrest.
"This is not an arbitrary, let me pick on you because of how you're dressed," Bennett said. "This isn't stop and detain. We add a dose of sensitivity to all that."
Modeled after Israeli airport security, TSA started using behavior detection officers in 2006. In November, USA Today reported that fewer than 1 percent of the people stopped in airports due to behavior detection were actually arrested.
In addition, TSA will be deploying multiagency teams known as Visible Intermodal Protection and Response to airports in St. Petersburg, Sarasota, Tampa and other arrival points for added security.
Tampa International Airport officials expect a 35 percent increase in passenger traffic due to the Super Bowl.