Took this picture for my little niece, Sydney. These signs crop up all over the place. They're not nearly as useful as the acorn posts, because they don't tell direction, but when you're looking at so-so maps from a book (and occasionally at an ordinance survey map), they're a good bookmark for where you actually are. 

Not sure if there's a connection between this Sydney Cove, and the Sydney Cove where Australia's first white settlement was established.