When I got into the sign business, I was taught to give dimensions as height x width. This was for a large company that primarily dealt with electrical signs, so most signs were landscape-oriented rectangles. So that was the preferred format used by the art department, manufacturing/production, vinyl department, etc. A few 'rules' were:
1) Be consistent and provide dimensions as height x width, regardless of the shape of the sign. This was a company-wide practice.
2) Don't leave dimensions open to interpretation (aka: an opportunity for a screw-up). Always indicate the height and width on all dimensions given. If a sign is four foot by eight foot, it was always given as 4'-0"h x 8'-0"w (not 4'-0" x 8'-0").
3.) All dimensions should be provided in a consistent manner. Either 4'-0"h x 8'-0"w or 48"h x 96"w (not 4'-0"h x 96"w......and definitely not 4' x 96"...that's a recipe for disaster).
Dimensions for smaller signs could be provided in just inches, but larger signs were generally always provided in feet and inches. Reason being is if you surveyed a pole sign that was 12'-0"h x 18'-0"w and the overall height was 85' or some such thing, writing 1,020" is a bit silly.