The correct answer to this open question is the following.
My draft of the sign that would be placed at the main entrance of COSTO stores is this.
Dear customer,
As part of our policies, COSTO respectfully informs you that to enter the premises you are required to wear a shirt and shoes, keep your children with you at all times, and your bags and briefcases will be checked for security reasons with your permission.
We kindly ask you to cooperate with us in order to have the best shopping experience with us.
Thank you for your comprehension.
These kinds of signs are understandable in shopping premises like COSTO or other supermarkets. There have been some incidents inside the stores that could have been prevented if some measures like the above-mentioned could be taken.
That is why is positive that the management of the stores ask their consumers for these minimum requirements to have a nice visit where everybody feels happy and safe.