I'm guessing that app allow you to discover LTE cell towers and it found a few. For me, a signal strength of -85dBm can be considered 4-5 bars and very good. Above -100dBm is acceptable, but won't get you the best throughput. -105dBm or lower tends to be 1 to 2 bars and not very good speed and lower than that is when your signal will began to cut out.