Good Vikash
Parsing of the subject itself can be something like
[\t\r\n]*incident \[sd5\] ACKNOWLEDGMENT:*[\t\r\n]
You need to use simple regular expression pattern. Here is the link for example of common one
But the question is what do you want to do with it?
Setup the category, assign to specific group, define the reporting method or other attributes
The main principle of those rules is to be able to define those criteria at the ticket creation.
Regards,
/J