This is the flag for the Socialist Party in Uruguay. They had a memorial/rally/street gathering that day for a recently deceased party leader. I only caught the beginning when people were starting to assemble - it struck me as very orderly, as everyone formed a long line. The flags and banners in the previous photo were for sale at the rally. I caught these two later that day along the waterfront.

Judging from the number of these flags draped around the city, Montevideo has many sympathizers. I didn't see many in the interior of the country.