I know that this is an unpleasant thought
BUT unfortunately it's one that SHOULD BE DONE. Let's look at the 2 different
categories.
Dealer - Insurance for dealers can usually be done through regular
inventory insurance. Each company handles it a little differently, BUT
make sure you have the transportation clause in your policy. This insures
the merchandise while being shipped and ELIMINATES the need to put insurance
on any packages that you ship out.
Collector - If you don't SELL posters, you can cover your collection
with a rider on your home insurance policy, called a floater. Insurance
companies have problems placing a value on a collection AFTER it's lost
so it's VERY IMPORTANT
make a list of your collection. Put a value
on each poster, preferably from one of the price guides where you have
documentation of the value of the poster. (that's the fun part). It's
actually better to even take a photo of each to attach to the list. If
you have a very large or very valuable collection, it's better to get
an actual appraisal. Submit the list to your insurance agent and keep
1 or 2 copies in a safe place.
As your collection changes, periodically change and resubmit your list.
Some companies only want you to keep an updated list and proof and don't
need a copy for themselves. The insurance policy then covers them as personal
property.