Source: https://www.flickr.com.Uploaded to Flickr by Florian Hardwig and tagged with "indigo". License: CC BY-NC-SA.

I had a feeling that these counterless letters filled with rainbow patterns might be typographic, i.e. prefabricated, as opposed to custom drawn (note to self: when in doubt, Indigo,a rather obscure design from the phototype era. He also pointed out the similarity to Rainbow Bass by Saul Bass.