StreamDeck has a built-in Icon Library, which allows you to add a custom icon from a list of pre-made icons to your StreamDeck keys. Anyone can add icons they've created to the Icon Library!
Stream Deck Icon Packs
You will find the Icon Library in the StreamDeck app if you select one of the keys and then click the small (+) icon (or select Open Stream Deck Icon Library under the small arrow icon) in the property inspector:
This will open a new Stream Deck Icon Library window with a list of available icon packs.
Stream Deck Icon Library
StreamDeck already ships with a number of icon packs, but you can also create your own. Icon packs let you distribute your icons to other Stream Deck users. An icon pack is a bundle containing your icons with some additional information to make it easier to find in the Stream Deck Store.