Unfortunately this seems to have been hotfixed overnight.
Currently there is a bug that allows you to stack Enchanted Sigil: Innovation. This allows you to potentially gain thousands of spell power or attack power.
How it works:
- Have only one sigil in your inventory (this includes bank)
- Activate the sigil
- Log off for half an hour (the cooldown of the item)
- Craft a new sigil
- Activate the previously crafted sigil
- Rinse and repeat as desired.
I've heard some say that it invalidates your Warcraft Logs, so use at your own discretion.