To find out the modem signal reception level, open the Network Setup → Status → System Log page:

In the appeared log you need to find the AT commands and the answer to the CSQ command:

For example: +CSQ: 23,99^M

The first number in this answer (23) is the signal quality.

Value RSSI dBm Quality 2 -109 Bad 3 -107 Bad 4 -105 Bad 5 -103 Bad 6 -101 Bad 7 -99 Bad 8 -97 Bad 9 -95 Bad 10 -93 Normal 11 -91 Normal 12 -89 Normal 13 -87 Normal 14 -85 Normal 15 -83 Good 16 -81 Good 17 -79 Good 18 -77 Good 19 -75 Good 20 -73 Excellent 21 -71 Excellent 22 -69 Excellent 23 -67 Excellent 24 -65 Excellent 25 -63 Excellent 26 -61 Excellent 27 -59 Excellent 28 -57 Excellent 29 -55 Excellent 30 -53 Excellent