I'm not sure how you set icons in Nautilus to use emblems by default, but adding an Ubuntu logo emblem to the Human icon theme is trivial.
A link needs to be created between /usr/share/icons/Human/scalable/places/start-here.svg and /usr/share/icons/Human/scalable/emblems/emblem-ubuntu.svg A emblem-ubuntu,icon file should also be created.
Just tested it here and was able to add the emblem.
I'm not sure how you set icons in Nautilus to use emblems by default, but adding an Ubuntu logo emblem to the Human icon theme is trivial.
A link needs to be created between /usr/share/ icons/Human/ scalable/ places/ start-here. svg and /usr/share/ icons/Human/ scalable/ emblems/ emblem- ubuntu. svg A emblem-ubuntu,icon file should also be created.
Just tested it here and was able to add the emblem.