From Melvor Idle

A template for quickly building upgrade links with icons. For example, {{UpgradeIcon|Dragon Pickaxe}} becomes Dragon Pickaxe (upgrade).svg Dragon Pickaxe

Also allows for overriding the link text with a second argument. For example, {{UpgradeIcon|Dragon Axe|The Best Axe}} becomes Dragon Axe (upgrade).svg The Best Axe

For a complete list of options, please refer to Template:Icon.