How do I hide the number of unread messages in the bin?

Just to add, you can't hide the number as long as there are items in the Bin.

Mail > Settings… > Accounts > Mailbox Behaviors. You can choose between erasing after one day, one week, one month or when you quit Mail.

Right Click the " Bin " and a Sub Menu should be presented

Question though.

If the message is in the " Bin " it is ready to be removed as in deleted - right.

Why would the User place Unread e-mails in the " Bin " if the intention was to actually Delete them

Follow advise from previous Contributor

But still do not understand why Unread messages are being put n the " Bin " unless these are Designated by the User ( you ) as Spam Messages

Normally and if the user has enabled Junk message filter on Apple Mail

Then the messages maybe moved to Junk Folder upon receipt.

Then, just using the Erase Junk