CV,
I always assumed that a pilot calling 'Field in sight' was implying he wanted a visual approach. Got caught out by some idiot making the call, and when I cleared him for a visual approach he replied 'Thanks, but we'd like to stay with radar for a while'.
After that I always asked 'Confirm you are requesting a visual approach?' when a pilot volunteered some meaningless comment like 'Fully visual'.
Advice to pilots: when you have a request, (not just for a visual) state it clearly and plainly. That way ATC can get working on it straight away, without having to second guess, or ask supplementary questions.