The correct response is, "It's a red warning flag that indicates to rescue personnel on the outside that the inflatable slide is armed."

Rescue workers contemplating a breach of a main door need to know if the inflatable slide is armed, which could pose quite a hazard. The slide is normally armed at all times throughout the flight. However, there are situations where emergency personnel must open a door from the outside; removing the strap is a signal that the flight crew has disarmed the slide, and the door is OK to breach.

Ahh, looks like a good number here are well-versed in commercial flight safety. Well done, SF.

Nodum.org

Well, when you have been in " the buisness" as long as I have . . .

It seems that Boeing has gotten smarter over the years. The airplane I am on (777) the slide will not deploy if the door is opened from the outside, even if the door is armed.