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>.
🎉 Copied!
@startuml
title: <size:20><&heart>Use of OpenIconic<&heart></size>
class Wifi
note left
Click on <&wifi>
end note
@enduml