If the Deaf couple noticed everyone else looking in their direction, maybe they should have glanced behind them to see what was happening. It could have been a car careening their way, a mad dog running at them, or some other dangerous situation. From the description, it was more dramatic than just people glancing at them while they signed to each other.
I don't think the police would be legally liable for damages. It's kind of the same situation where police have busted into the wrong residence looking for drug dealers based on information from an informant. The courts have previously held that if the police made the bust in good faith (even if it was incorrect) then they weren't liable.
An apology would certainly be a sign of good will from the department.
Cops are at risk if they just "tap someone on the shoulder" and that person whirls around with a gun for response. Also, if someone who has been pulled over starts reaching into a bag, how do you know they are reaching for a pad and pen, or a gun? Sometimes the cops who are too "nice" are the ones who get killed.
The sad truth is, the world can be a dangerous place and life isn't always fair.
