I was under the impression that signs requesting that people do things would be in honourific rather that humble speech, however so far I've noticed the opposite. Could anyone please explain why this is? Thanks in advance!
Will definitely need examples here, but in the mean time this may answer your question:
This is explained in great lengths in 敬語の指針:
But this seems to match your understanding of both forms, so without examples, can't be really sure about what you mean by "requesting that people do things" with kenjougo, sorry.