Could we changed the scope of this tag, so that it can apply to other objects, and not only to clocks ?
For example, it could apply as well to 'advertising' objects, but it likely could apply to more cases
And in that case we could rather write something like :
visibility=* is used in connection with publicly visible devices or features to display their visibility/readability.
-visibility=house Entity (or device or feature) is readable from up to 5m (targeted mostly for pedestrians, or bikers)
-visibility=street Entity (or device or feature) is readable from up to 20m (targeted for passers-by in for vehicles going slowly)
-visibility=area Entity (or device or feature) is readable from more than 20m (targeted for passers-by in vehicles going fast)