If you are one of them and you're running apache don't forget about default /icons/ alias. Anyone can use it to guess that you're using apache, for example:
Directory content can be different between apache versions, so it also may reveal which version you are using.
Apache 2.2 (icons/apache_pb.gif):
Apache 2.4 (icons/apache_pb.gif):
For more differences you can take a look in apache source code repository history:
You can disable this alias in the httpd.conf file, simply comment out the line:
Alias /icons/ "/var/www/icons/"