Strange characters on CiviCRM dashboard
It might be that the css of your theme clashes with the css of civi (there is a style rule to avoid repeating that icon, that might be overwrited by one in your theme).

As a quick test, can you switch to the default drupal theme and see if it's still an issue?

If not, you will need to modify your theme to add a rule so the background image for the icons doesn't repeat. Not complicated, but likely specific to your theme, so hard to give you a generic advice without knowing the specifics