Installer without icon resource
From NSIS Wiki
This is a "HowTo" to create an Installer that has no icon resource.
- Because you might want to let your User's System decide what icon to show, see this forumthread: 
- Because the Icon Resource adds additional overhead to any installer using it
How do I do that?
You'll find the easiest known method on the second page of the forumthread, but i'll post it here again:
First, download and install Resource Hacker  to your system.
Then add this compile time command line at the end of your .nsi script:
!packhdr "exehead.tmp" '"C:\Program Files\ResHack\ResHacker.exe" -delete exehead.tmp, exehead.tmp, icongroup,103,'
Of course you may need to adjust the path you installed Resource Hacker to.