When placed on top of and next to a Block of Redstone, Redstone Wire will not be seen on the side of the block. The Dust instead will act similarly as if it were on top of an upside-down slab, and connect; yet not show the texture. Although this technically doesn't really matter, as Redstone Wire would never need to run up a block, it would make sense that the Redstone Block would act as a regular solid block.