Sometimes the view of the sidewalk is completely blocked. In these cases, you should place a "Can't See the Sidewalk" label. This should rarely be used, so only place the "Can't See the Sidewalk" label when a sidewalk, ramp, or other accessibility problem cannot be viewed from any angle due to obstructions, such as cars.
Another rare case when you should use the "Can't See the Sidewalk" label is when a long stretch of sidewalk is totally blocked from view by a short wall between the road and sidewalk. Label this using the same technique as for extended missing sidewalks.