Personally I'm quite vocal so never any surprise with me. Normally along the lines of
oh fuck I'm cumming .
As for whether the girl has specified in her Enjoys whether she does CIM or not, I find that from experience,
in the moment things may change. So I won't necessarily pull out, but equally I'm not forcing it in at all. So it won't come as a surprise to her, and she doesn't have to get an unwanted mouthful either. No coercion.
And I apply this 'rule' in general, to both Civvies and WGs. I'm also mindful that a girl shouldn't in any way feel forced, so I'm aware of any body language which might betray that. If I feel any such discomfort then I withdraw as a gentleman should.