Traceflag 1102 causes 1105 errors to be sent to the errorlog. By default, 1105s are sent just to the client.
The result is similar to running "sp_altermessage 1105, 'with_log', true" although the traceflag raises the error with state 1 while sp_altermessage shows state 2.
The traceflag predates the sp_altermessage functionality.
Examples:
Errorlog entry from activating traceflag 1102:
00:0006:00000:00016:2014/01/22 10:45:29.42 server Error: 1105, Severity: 17, State: 1 00:0006:00000:00016:2014/01/22 10:45:29.42 server Can't allocate space for object 't' in database 'full' because 'default' segment is full/has no free extents. If you ran out of space in syslogs, dump the transaction log. Otherwise, use AL TER DATABASE to increase the size of the segment.
Errorlog entry from using sp_altermessage
00:0006:00000:00016:2014/01/22 10:45:29.42 server Error: 1105, Severity: 17, State: 2 00:0006:00000:00016:2014/01/22 10:45:29.42 server Can't allocate space for object 't' in database 'full' because 'default' segment is full/has no free extents. If you ran out of space in syslogs, dump the transaction log. Otherwise, use AL TER DATABASE to increase the size of the segment.