Well, you can set thier behaviour to "safe.
In the init. field of the soldier type this:
This setBehaviour "Safe"
If you want it in a trigger, give your soldier a name, let's say, LAPD (
) and in the trigger on activation field write this:
LAPD setBehaviour "Safe"
I think there is one more behaviour that make the soldiers put the weapon on thier back. Maybe "Careless"
And I also think there is an animation to this, But I don't know what it is. Someone else will tell you, I guess.