Shopify products can have either an "Active" or "Unlisted" status.
Active - Products appear in your store catalog and in search results
Unlisted - Products are still "Active" however they no longer appear in your public store catalog or search results
By default new products are created with the "Active" status, but you can configure Sign Customiser to create them as "Unlisted" if you wish.
How to set new custom sign products as unlisted
Log into your Sign Customiser account
Click on "Tools & Settings" -> "Integrations"
Click on Your Shopify integration
Click on "Edit Integration"
Change "Default Product Status" to "Unlisted"
Click "Save"