Covers do have an arrow up or down in te buttons - I think A LOT of people would be happy if this is customizable.
Please vote, prove I am right! 
Possibly a dup of https://community.home-assistant.io/t/wth-why-is-it-so-hard-to-add-home-made-icons/804496?
Could be also, but I would be already happy to use ani mdi icon