Weatherall is the most popular choice for External signage.  Weatherall has a thicker top layer (~.020) which provides for a much more durable finish.  Normal wear & scratching will not pass through to the sub-laminate, making the visual signs of age much less obvious.  This material is  U.V. stable, so it is ok to use in full sunlit conditions.  There are 3 other lines of Weatherall available, known as Weatherall 1, 2 & 3.  Weatherall 1 has the same properties, but it's finish is a brushed satin effect.  This is useful where reflected light reduces readability.  Weatherall 2 & 3 have a clear core for reverse engraving.  Weatherall 2 has a gloss finish, while Weatherall 3 is matte.