I saw this posted on the side of a gas pump in Pennsylvania:
If a fire starts, do not remove nozzle then back away immediately.
I'm sure many people will get exactly what this is supposed to be saying. Nevertheless, it doesn't say what it's supposed to say. If just spoken, it's ambiguous between the following two meanings:
1. If a fire starts, what you shouldn't do is remove the nozzle, and what you should do is back away immediately.
2. If a fire starts, here's what you shouldn't do: remove the nozzle and then back away.
The first is the intended meaning. I think the second is the more natural interpretation when spoken. But this is actually written, and there's one thing that settles which meaning it has: whether there's a comma or some other separation marker between 'nozzle' and 'then'. There isn't. That means that, as written, it clearly does mean 2 and not 1.