Although I can't read a word of Polish, I can interpret enough of this sign to realize that I'm in a square named for U.S. President Herbert Hoover. I assume that the naming of the square has something to do with Hoover's relief efforts in Europe during and after World War I.

"Hoover Square. The name was given in 1922 as a symbol of gratitude for the U.S. aid given to Poland that was organized by Herbert Hoover. 1992." (Translation provided anonymously.)