welcome to the forum, Richard.
embedding cloth or fabric items in casting resin is probably one of the
trickiest things to accomplish successfully with satisfactory results.
each fabric item will behave differently when saturated with a product
such as glue, varnish, polyurethane, epoxy or casting resin.
much understanding and experience with this process is very strongly
recommended before doing a project that you could possibly ruin with no recovery.
there are dozens and dozens of different types of epoxy and casting resins
that people use to embed items in. there are also hundreds of tutorials on the
net and YouTube on how to do it ~ some good, some bad.
my number one suggestion is to practice, practice and practice some more
if you have never poured epoxy or casting resin before.
as for the shoulder patches, I have seen many, many displays of articles such as
this in different forms. (and I'm sure you have also). embedding them in
plastic is permanent. you can not change it. you can not add or take away
any of the items. and if there is smoking in your bar, some resins will absorb
the tobacco smoke and turn yellow. (even if the resin says "will not yellow"
on the container).
my personal recommendation is to make a large picture frame with glass
so that you can add patches to the collection in the future.
I'm pretty sure that once you have it on the wall, you will get many contributions
to add to the collection.
POLICE PATCHES DISPLAY - YouTube