Enter some junk value into your .htaccess e.g. foo bar, sakjnaskljdnas any keyword not recognized by htaccess and visit your URL. If it is working, you should get a
500 Internal Server Error
Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request....
I suggest you to put it soon after RewriteEngine on.
Since you are on your machine. I presume you have access to apache .conf file.
open the .conf file, and look for a line similar to:
LoadModule rewrite_module modules/mod_rewrite.so
If it is commented(#), uncomment and restart apache.
To log rewrite
RewriteEngine On RewriteLog "/path/to/rewrite.log" RewriteLogLevel 9
Put the above 3 lines in your virtualhost. restart the httpd.
RewriteLogLevel 9 Using a high value for Level will slow down your Apache server dramatically! Use the rewriting logfile at a Level greater than 2 only for debugging! Level 9 will log almost every rewritelog detail.
UPDATE
Things have changed in Apache 2.4:
FROM Upgrading to 2.4 from 2.2
The RewriteLog and RewriteLogLevel directives have been removed. This functionality is now provided by configuring the appropriate level of logging for the mod_rewrite module using the LogLevel directive. See also the mod_rewrite logging section.
For more on LogLevel, refer LogLevel Directive
you can accomplish
RewriteLog "/path/to/rewrite.log"
in this manner now
LogLevel debug rewrite_module:debug