© 2018 David Roesel, taken with EOS T1i above Nové Mlýny
An explanation for my foreign friends: PF is an abbreviation of Pour Felicitér meaning (or at least meant to mean) "Happy new year!". Although the words are French, they are only used this way in Czech and Slovak for some reason. If French is too uncomfortable, which I understand, just imagine a Happy new year! sign.