Symptoms

The top navigation bar displays this:

Instead of this:

Cause

The icons are actually fonts, obtained from the Atlassian Icons font pack. Somehow, Internet Explorer is not permitting downloads of fonts from Confluence due to the Security Configuration in Internet Options >> Security

Resolution

• In Internet Explorer, navigate to Tools >> Internet Options >> Security
• Do the following for all zones:
  1. Click Custom level...
  2. In the resulting Security Settings prompt, look for the Downloads section, and set Font download to Enable.
  3. Click OK and then Apply (remember to repeat these 3 steps for all zones)
• If this does not work, then there could be other reasons causing this. Best would be to try to download the font pack manually via: http://<yourConfluenceURL>/s/en_GB-1988229788/4226/d7686547091e645d7b0285207c0b86be721c74eb.1/5.0/_/download/resources/com.atlassian.auiplugin:aui-experimental-iconfont/atlassian-icons.ttf to see if indeed, Confluence is serving that font pack correctly.