This is just a case of "abort mission right the fuck now", yeah? Run away, whatever. We can use stop because this one gotta be something we need we got to act on fast. Like, say, if someone suddenly goes crazy on us but it's not really a good idea to call 'em out on it.
How about this?
[holding his hand out, palm open, then closing it once, opening again, and moving his hand to the side]