Furuno FAR-2807(-D) series Operator's Manual page 177

Note 5: AIS symbols are shown in dotted lines in the following cases:
- No water or ground tracking speed of your ship, or there is no speed
data. All AIS symbols are shown in dotted lines and the message "NO
CPA/TCPA for AIS" appears (in red) in the Alert Box.
- No water or ground tracking speed received from AIS target, or no
speed data from AIS target. The symbol of the corresponding AIS
target is shown in dotted lines.
Note 6: Other AIS symbols that may appear are shown in the table below.
Symbol
+
+
Note 7: The CPA and TCPA of SAR aircraft data are not available, and are
shown as ***.
Meaning
Real AIS AtoN
Virtual AIS AtoN
Base Station
Airborne SAR aircraft
AIS SART
4. AIS OPERATION
4-3