The blindingly bright blue lights and red lights strobed by cops to overwhelmingly signify their presence and intimidate others; a highly visible, attention-getting representation of authoritye. Respect it (as Officer/Deputy Cartman would demand).
Not to be confused with black light, disco lights, candle light, or Coor's Light. The police are the only ones enjoying this kind of PARTY in their own power mad, sadistic, or Barney Fife way. You can witness for yourself the giddy celebration following a full-out domination and capture event on many episodes of the 'reality' TV cop shows.
"PARTY LIGHTS are evil tools that scream out: "Trouble !!" -- quite possibly for you, if it appears the PARTY is coming your way."
RAY: "I see PARTY LIGHTS up ahead; better slow down to the speed limit."
JAY: "Well, I see 'em in my rearview, too. I think we must be invited to the PARTY."