If you haven't, there is a riveting chapter about a military espionage operation that took place off the Kamchatka Peninsula. The operation was highly risky, but the payoff was huge -- it allowed one group of people to listen to another group's communications, which were passed in plain language "in the clear." (Based on the seemingly-obvious assumption that no one could do what had in fact been done).
When I saw this sign while walking across the Longfellow Bridge yesterday, I stopped to take a picture and paused for a quick moment of tribute to the men who left Mare Island (near San Francisco) to undertake these operations.
No one will ever know their names. But we all ought to be grateful for what they did.
If you're wondering what's special about that sign, just remember this: Sometimes the thing you're looking for is hiding in plain sight.