Final answer:
Maximum height signs indicate the tallest height a vehicle or cargo can be to safely pass under an underpass without causing damage or accidents.
Step-by-step explanation:
When approaching a low underpass, it's crucial to be aware of height limitations to prevent accidents or damage. The maximum height indicated on the sign is the tallest your vehicle or cargo can be to safely pass under without hitting it. If a sign reads 'Maximum Height 12 ft', then any vehicle or load exceeding that height must not enter. It's essential for the safety of the structure and your vehicle to adhere to these restrictions, much like the weight limits on a bridge or capacity limits in a building.