There's a Costco right around the corner from me and I never even been in it. I have nothing to buy there and no need to buy in bulk. Same with SAM's Warehouse. I don't even know what this particular store's policy is or if they have a sign. Maybe I should drive by it and check just out of curiosity.
That aside. Concealed Carry = What they don't know doesn't hurt them and enhances my shopping experience.
Who are they to tell me what makes a good shopping experience for me? It surely isn't shopping in a store that doesn't allow me to practice my rights.
All other places of business seem to be doing just fine allowing me to carry a firearm in their property.
What does Costco think that telling law-abiding shoppers they cannot carry a firearm in their store is going to do? Make a criminal-minded person obey their sign??