Interesting catch!
I agree it would be nice to know the story behind but until someone is going to tell us, we may construct our own. Something like...

Once upon a time a man arrived to Vila do Conde. His wife sent him to buy some groceries for their home and farm. Unfortunately there wasn't a single store, and he was already tired of walking.

Therefore he stopped first passerby and asked where the locals usually go for shopping. He was told that once a month they organize themselves to go to nearby larger town.

"Why only once a month," asked the man? The passerby said there is only one vehicle in Vila do Conde. It's a big truck that belongs to a man who the rest of the month works driving all around the whole Portugal, and only once a month returns home. Therefore, the passerby also mentioned, the big problem is if we forget something or make wrong predictions of their next month needs.

A brilliant idea crossed the man's mind when he heard that. He returned home and shared the idea with his wife, of course, after he survived her yelling because of returning home without groceries.

A few months later man opened a first grocery shop in Vila do Conde which was on the exact place of current supermarket. As it was a great-grandfather of the current supermarket owner he put this sculpture in front of the entrance door, representing his great-grandfather first arrival to Vila do Conde looking for the shop.

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