Judging by the location of these mobile cameras I would suggest that the answer and advice is to beware when on the A27 or A23 or there is the other answer slow down.
Wasnt a Chief Constable recently quoted as saying that the speed limit is set eg 30 mph and anybody in his area exceeding it even by 1 mph will have action taken against them Slightly OT but may be of interest to some on here but Sussex Police use a plain unmarked Black Audi 4x4 in that area...