Weld County School District 6 says Manning's number 18 has been banned because of the number's gang affiliation. The ban has been in place for four years as part of its dress code for all schools.
The District says the ban has not been an issue until this year, when Manning was given this number by the Broncos.
District spokesman Roger Fiedler told 9NEWS Crime and Justice Reporter Anastasiya Bolton that he's heard from a number of parents wondering about the number 18. Most, he said, were understanding once he explained why the number was banned in school.
"We're really trying to eliminate or minimize the presence of gangs in our schools," Fiedler said. "There are gangs in the community. We take a very aggressive stance in keeping that activity and that behavior off of school grounds. Part of that is banning some of the colors numbers and others insignia that are closely identified with gangs."
The student dress code outlines proper attire for all students. It bans trench coats, exposed undergarments, red or blue belts and shoe laces. No team jerseys or belt buckles that display the numbers 13, 14, 18, 31, 41 or 81 are allowed.
"Since we instituted the dress code policy, we've heard from principals and our director of safety and security that the number of gang incidents in schools has been decreasing because of taking stances like this," Fiedler said.
"Our thing is wear those jerseys after school; wear those jerseys on the weekend, especially on Bronco Sunday. Wear them," Fielder said. "Just during the school day, during those hours, our focus will be on teaching and learning. We want to make sure we're not getting into the situation where gang members are allowed to display their affiliations. "
Rules apply to all schools - elementary through high school. Greeley Police say gangs are generational, so age does not really matter.
"It's not uncommon to find children wrapped in bandanas shortly after birth. They're raised like that through life," said Mike Prill, Greeley Police Gang Unit Detective who's worked the beat for 14 years.
Prill says the gang issue here is no worse than in any other similar size city. The wrong person caught wearing the wrong thing can get hurt.
"Misperceptions of someone's memberships and assaults that occur from that do occur," Prill said. "People aren't certain if someone walking by, [wearing a] blue number 18 jersey, might be a member of 18th Street. Confrontations occur frequently where they misperceive the individual as a gang member, when in reality they're just a student out on lunch."
Greeley Schools aren't the only ones with gang-related clothing restrictions.
Adams 14 Schools told 9NEWS their dress code prohibits students from wearing clothing with "gang-like graffiti" or that reflects gang affiliation.
Adams 12 says students aren't allowed wear any professional sports jerseys of any kind.
Jefferson County School District, Douglas and Denver public schools don't have specific restrictions like Greeley. But principals can address the issues as needed.
Douglas County prohibits wearing clothing showing gang affiliation, but Manning jerseys are not banned.