I am using these icons in my next DMs Guild release. (And I hope other Guild authors do too.)
What's most useful about the icons is how they work like traffic signs. They signal the reader as to the type of content on the page, and in the case of the adventure icons they allow the DM to quickly determine if an adventure is in the proper adventure tier and how long an adventure will take.
Very, very useful.
[5 of 5 Stars!]