Posterity? Vanity? History? You make the call. But while this bright blue "Built in 1890" tag most certainly belongs to the building upon which it's affixed, I kind of like the implication here that it's actually the number 302 that was built in 1890.
Whether it's to denote a historical event or announce that so-and-so lived in such-and-such address at such-and-such time, sticking plaques on buildings is one of the easiest ways we've devised to pass on a bit of local history to others. Personally, I'm all for such homegrown geekery. Not only do I get to learn a bit a trivia, but it's also like someone leaving little notes for me all over the city.
However, there's always something lacking in plaques where all I'm given is a date. Now, there are some exceptions. When a year is carved into a foundation stone, that seems to me like a logical signing off, a way of saying, "Yup. Finished this one. Better sign it." But these modern-looking afterthought signs are a weird affectation to me. Who decided that its being built in 1890 was significant enough to warrant its own special sign? And am I the only one who is reminded here of those omnipresent "On this site in 1897 nothing happened" plaques that you see in all sorts of strange places throughout the world?
If nothing else, this does bring back fond memories of my favorite plaque hoax of all time, one Father Pat Noise, who lives on in secret notoriety on the O'Connell Bridge in Dublin. Now there's a piece of history I can get behind. Even though, like all that stuff in 1897, it never happened.