What is the distinction between Sign 3.27 (blue circle with red border and red 'X') and Sign 3.28 (blue circle with red border and single red diagonal slash)?

1. Sign 3.27 prohibits both stopping and standing; Sign 3.28 prohibits standing only, so a halt limited to boarding, alighting, loading or unloading stays lawful.
2. Sign 3.27 applies to buses; Sign 3.28 applies to passenger cars.
3. Sign 3.27 allows parking on weekends; Sign 3.28 allows parking on weekdays.
4. Sign 3.27 is a warning sign; Sign 3.28 is an informative sign.