I would go with, what I think most would agree, that the arrow is indicative of the signal or current flow. If the manufacturer places an arrow on the product, that would indicate to me that the intention is for direction of signal or current. But truthfully on a fuse, I doubt any discernible difference would be present, in my opinion of course. But if they have an arrow on it, they have a reason for doing so and I would still adhere to that as installation direction.