Just about every year, Halloween brings campus disputes over costumes built around ethnic or racial stereotypes. Several universities this year are trying -- in advance of Halloween -- to discourage offensive costumes. The University of Colorado at Boulder has put posters up on campus  that show members of different racial and ethnic groups -- and some of the stereotypes that have been the basis of costumes. The tag line for the posters: "You wear the costume for one night. I wear the stigma for life." The University of Minnesota-Twin Cities sent a letter to students urging them to avoid costumes that perpetuate stereotypes, The Star Tribune  reported.