I was looking through some old posts and I found this thread from 2017 here. I volunteered four years ago to help with making these. Is this still something that would be useful to the site? I'm looking for a valid excuse to make more signs. 
Yes it would be as I can only do so much along with updating/maintaining both AARoads and Interstate-Guide. During the last couple of years, the sign graphics have been made by just me with AI. I have replaced some of those old graphics in the OP as I go along and revamp or update older pages.
myosh_tino was a tremendous help with creating templates for route markers. Zeffy also provided a lot of assistance with the guide sign graphics in 2013-15.