In this episode Harm teases Meg about the "hook'em horns" hand sign.
In Italy, Germany, Portugal, Brazil and Spanish-speaking countries, "horns" are a metaphor for suffering the infidelity of a partner, not limited to husbands in modern usage. The gesture of the horned hand can be used to insult the cuckold; the Italian translation, cornuto literally means horned (This sometimes causes confusion in Italians who are learning English and encounter the word horny). In some cases, "cuckolding" is a means for the husband to express same-sex desires through his wife and/or directly with the additional participant.
However, the meaning Meg meant to convey was support for her alma mater the University of Texas, which uses the "hook'em horns" to symbolize the school's mascot, a longhorn bull.