If it looks right, no one will pull out a pocket level to check to see if it is.
I had hoped that someone in this community might be able to point me to some published reference for exterior and/or parking garages. Although I have the end-users design standards, they all deal with size, font, distance, etc..., not the practical aspects of making it "look good" when it goes up.
I've had more than one customer come in with a level to check if a
sign is truly level. In one case it was because the
sign was rectangular but then the end had a large swoosh as part of the logo. It made the
sign look left-heavy and even though I knew it was level, it did look off-level. It was pretty annoying. Anyway, the customer stood there and stared at it, left, came back with a little torpedo level and checked it. Then they asked for my level and checked it again.
In another instance, I had a girl that worked in the office I was installing in come out with a torpedo level and a tape measure and climb up on the desk the letters were installed above. She proceeded to put the level on various letters because 'they looked off' (a lot of curved letters next to straight letters). She then started measuring the distance between letters and said that it was wrong because some were closer than others. Obviously it wasn't wrong, it was put up with a pattern and it was just how the kerning was. She was up there so long checking it, I took a picture and texted it to my customer (another
sign company). Even though the letters were correct, the girl insisted they be removed and reinstalled while she watched and approved the various ones she thought were spaced wrong or that looked off-level. I told her that was fine, but I would need to confirm with my customer (the
sign company) that I do that, since I would be charging them extra. The girl was fine with it, I called the
sign company, they nearly went ballistic but said if that's what she wanted then do it and they would back-charge them. One of the most annoying/frustrating installs I've ever done.
As far as a published reference, I highly doubt anything like that exists. A slanted wall or beam doesn't mean a
sign should be installed off-level.