The signs were seen during Friday night's varsity game against Plano East Senior High School.
Flower Mound parents are keeping mum about the incident, not wanting to talk about what some call a "misunderstanding."
However, the racial implications have become national news, thanks to social media -- a photo of the signs immediately started trickling through Twitter accounts with retweet after retweet.
Plano East students and parents hope the students who held the signs are reprimanded.
"I thought that was very disrespectful, to be honest," said Plano East senior Allison Compass. "I didn't think a school would do that or I didn't think a school would let their students do that."
Plano East senior Madison Compass says their principal addressed sportsmanship at a pep really Tuesday morning.
"‘The way we should win is winning with class,'" she said. "He was repeating it a lot and everybody was applauding him."
The Flower Mound basketball team's coach tweeted, "Unacceptable. As head coach at FMHS I offer our full voice apology. I will pursue this fully. No place for this."
Flower Mound is part of the Lewisville Independent School District, and the interim superintendent, Dr. Kevin Rogers, released a statement Tuesday, saying, in part, "I want to be clear that this type of incident - however it has been perceived - has not and will not be tolerated in LISD…Ultimately, please know we have the highest respect for the students, staff and community of Plano East High School."
Lewisville ISD officials haven't said whether the students have been identified and punished in any way, only saying that it's an ongoing investigation.
"Those kids, if they did do something like that, they should be reprimanded for it and the district should just move on," said Joe Brown, whose nephew plays basketball for Flower Mound.
Some Flower Mound students have said on social media that the signs were part of a chant about the school's colors, navy, silver and white.