Affects the Icon to be shown, there are several versions of this:
#showcooldown spellname <--Shows a spell icon and it's cooldown
#showcooldown itemname <--Shows an item and it's cooldown by name
#showcooldown BagId slot <--Shows an item and it's cooldown by bag slot
#showcooldown InvSlot <--Shows an item and it's cooldown by inventory slot
#showcooldown <--Shows an icon and a cooldown dynamically (See Notes)
Selecting the "?" icon will use the icon for the spell/item/slot. This can be overriden by manually choosing an icon.
If you don't know the spell, don't have the item, or the position you specified on your character or bag is empty, the button will show the default "?" icon.
Other data affecting the button's appearance will be pulled from this as well, such as the green border around equipped items, the number of items you have, the number of reagents for the specified spell you have, etc...
The click action of the button will not be affected by this, you still need to use the commands to make the button do something.
Any successive metacommands to define the icon or tooltip will be ignored
This does not affect the tooltip of the macro. If you want to specify both the icon and tooltip, you should use #showtooltip.