How can I uninstall Trend Micro Safe Surfing once the app has been deleted from my Mac OS X?

Check to see if there's such a folder as either

/Library/Application Support/Trend Micro

~/Library/Application Support/Trend Micro

and if so, see if either contains an uninstaller.

Failing that, download the demo version of the app from Trend Micro, and try the uninstaller that it should contain.

If all else fails, the manual way would be to use something like EasyFind and search for anything with "com.trendmicro" in the filename (you can use Finder, but be sure to include system files and invisible files in the search options). Pay particular attention to the folders

/Library/LaunchAgents

/Library/LaunchDaemons

~/Library/LaunchAgents

~/Library/Internet Plug-Ins

~/Library/Preferences

Further to that, have a loock in Safari > Preferences | Extensions and see if the Trend Micro Toolbar extension is installed. If it is, disable it and then hit the 'Uninstall' button in Safari's Extensions preferences pane.

Check here in the Finder to be sure it's gone:

~/Library/Safari/Extensions/iTISToolbar.safariextz