When told “no humans”, generated exclusively images of humans

Asked firefly to create a logo for a fictional futuristic organization called Nemesis Degense Corporation. When it returned me images of humans, I added "no humans". No change in results. I tried "no people", "exclude humans", "logo only", and other similar verbage, but still kept getting only images of humans.

How do you get it to listen when you tell it not to do something?