The feature described here is a useful functionality to debug in-call issues and easily search for specific events within the system logs. When a particular issue occurs you can press the pound key (#) on the handset to log that event into the syslog:
In this example the user with SIP account 500 using the handset identified with Pmid 00001 pressed the pound key (#) during a call:
2017-11-16T13:43:28Z 172.16.18.12 000413610ff5 Umber 00512 -[ Call Marker user 500 Pmid:00001 CallId#0007] '
This feature will only work if you press the pound key (#) during a call.