There is currently no way to disable the onboard LED on the Notecard. However, the power consumption of the LED is minimal and, in a battery-powered device especially, the Notecard should be in periodic or minimum mode which will lead to the Notecard only flashing in brief intervals when it’s transmitting data.
I had a regular red blinking LED on my notecard.
Ended up here, while trying to figure out what it indicated.
I went away thinking it had something to do with DFU.
I played with the DFU settings and it keep blinking!
I would like to save any Notecard noobs some searching, and add that the red led (on a WBNAW and maybe others) has a short blink regular blink when i am connected to the In-Browser Terminal!