。！
Workers of the world, unite!
Literal
All-nations' workers [vocative-よ]. Unite [classical imperative-せよ]!
The famous closing line of the Communist Manifesto, in Japanese translation. 万国 ('ten-thousand nations') = 'all nations of the world.' The vocative よ marks direct address (like 'O workers!'). せよ is the classical imperative of する — archaic, formal, and highly emphatic, appropriate for slogans and rallying cries.