If you are using specific searches you have bookmarked or saved, the postal code might be stored in the page URL of your searches; or at least it was possible to do that in the past.
One place you can see this postal code is in your search results when you sort by distance. The country or postal code should appear as a link in the search results if you are using a desktop browser. Previously that link was in the upper right, but now I see it on the left side of the page just below the category tree where it says "Postage to [postcode]".