I lived in Hoboken during the 50s. Each park in the city had a hot dog wagon and a yum yum man. The yum yum man had an orange push cart that housed a freezer containing different flavor Italian ice. One was yum yum. It was the best. 10 cents. Years later in the 80s i was at the Seaside boardwalk by the carousel on the south end. In there was in lemom ice counter that listed yum yum among it's flavors. I couldn't believe it. I went to get some and the attendent said it wasn't carried anymore because no on purchased it. ( No one could identify with the flavor ). I guess it was a Hoboken thing.
So maybe it's still around somewhere.