I'm glad to see this is going to cover other than film posters.
There are very few serious film poster collectors and dealers who
do not eventually branch out into other areas. It is, after all, the posters
that are of interest.
One of my own favourite non-film posters is for a glass ringing act from
around the 1910s or so.
The connection is that they used to perform in the local hall where my
mother lived as a kid, in what was later to become the small town's first
movie theatre.
Phil E.