Came upon this post during my travels. Jonathan Lewis reveals how to write a string to the Alert Log, Current Session Trace File, or Both. Also a few misc functions are included.
dbms_system.ksdwrt(1,'test')
writes to alert log
dbms_system.ksdwrt(2,'test')
writes to session's trace file
dbms_system.ksdwrt(3,'test')
writes to both
see also
dbms_system.ksddt - writes a date-time stamp
dbms_system.ksdind(N) - indents text using ":' characters