The photo shows a wall with graffiti that says "Uzay Metro Torbacı" The joke is a play on words, as "uzay" (space) is combined with "metro" (subway), and "torbacı" is a slang term for a drug dealer. So, the whole sentence can be interpreted as "Space subway drug dealer". The humor comes from the unexpected and absurd combination of these words. The joke also points out the fact that people sometimes use slang or informal language even when referring to seemingly serious or abstract concepts like space travel.