There will be a flag for every perfidious person on the Day of Judgment, and it would be said: Here is the perfidy of so and so. (Using translation from Muslim 1736a)
عَنْ رَسُولِ اللهِ ﷺ قَالَ «لِكُلِّ غَادِرٍ لِوَاءٌ يَوْمَ الْقِيَامَةِ» يُقَالُ «هَذِهِ غَدْرَةُ فُلَانٍ»