OpenIconic is an very nice open source icon set. Those icons have been integrated into the creole parser, so you can use them out-of-the-box.

    You can use the following syntax: <&ICON_NAME>.

    title: <size:20><&heart>Use of OpenIconic<&heart></size>
    class Wifi
    note left
      Click on <&wifi>
    end note

    It also works with salt, the graphical interface designer.

      Login<&person> | "MyName   "
      Password<&key> | "****     "
      [Cancel <&circle-x>] | [OK <&account-login>]

    The complete list is available on OpenIconic Website, or you can use the following special diagram: