Allusions in the artwork. Particularly referring to the Incredible String Band, for whom BoC have a great deal of respect, and whom they apparently see from time to time. The lyrics section reveals that they have sampled the ISB occasionally; there's the old track "ithcus sound", a possible reference to the ISB track "ithkos". There's a general similarity in mood between Geogaddi and such ISB songs as "Waltz of the new moon" (HBD). It has also been observed that the title "Geogaddi" might in part refer to the ISB song "koeeaddi there" (HBD again).
One interviewer comments that the front covers of the ISB's "The Hangman's Beautiful Daughter" and BoC's "Music Has The Right To Children" would make "a nice pair":
However, but there is a far more striking similarity between the back cover of the ISB album, and some of the pictures of BoC available elsewhere; if this is any more than coincidence, and it may be no more than that, it makes a nice tribute to the ISB:
The next pair aren't all that similar, except in their mood, but here they are anyway: