Final answer:
Roubieu's graffiti work is most likely on display along subway lines and on train cars.
Step-by-step explanation:
Street art and graffiti are forms of visual art created in public locations, usually executed outside of traditional art venues. Artists often use this form of art as a platform for expressing social and political issues. Roubieu's graffiti work is most likely on display along subway lines and on train cars, as these are popular locations for street art and graffiti.