One of the plaques depicts the first person across the bridge via that conveyance. The person to cross the bridge in a wagon was Emily Warren Roebling, according to our guide. Without her, the bridge may not have been completed. Read up on her role.
I love the juxtaposition: lock, lox, and nevertheless, there are padlocks just above the sign. If the expectation of locks doesn't make sense to you, look up https://en.wikipedia.org/wiki/Love_lock. They have to be removed because the cumulative effect of so many locks adds a lot of unnecessary weight for the bridge to support.