It worked for you, but not for me yet.

Probably I did not drive enough of your maps then
Strange, very strange.
Are you sure your solo play maps have used the urls everywhere, and not the "local" instances of the signs?
Because I just noticed In the editor you have to be very careful... precisely not to click on the local instance of the sign - as this would not trigger the download then.
I cleaned the cache, tried A01 solo again, and there were no signs. Only some of your other artwork like the WTC bakcground and title, or advertisements like "Alienware Arena".
Then I tried with an own map, put sign only on my dropbox (Attention, it gets downloaded in the editor only if you put it to the public folder, and use a http:// instead of https:// link)
Then I cleaned the cache, and when I started this map solo, it downloaded the sign (there was a indication at map launch), like it should be.
If you like you can try it:
https://www.dropbox.com/s/k39np1uqpywv4 ... st.Map.Gbx
From the tries with the https:// links, there were also .dds files left,
but they contained a copy of the DropBox page which points to the actual download.

Those got "displayed" totally black in the editor btw.