Uncle Sam is very fucked off and pointing at you with his finger and giving the big middle finger at the same time! He is such angry badass. The illustration is a parody of famous "I Want You" army recruit propaganda poster.
Uncle Sam is pointing you with thumbs up. He is giving very positive vibes to you. This illustration is a variant of “I Want You” pre-war propaganda poster, originally made by James Montgomery Flagg.
Check out other variants too when he is wasn't not so happy pal.