All neighborhood pubs in Belgium used to have such a “savings-cabinet”, as you see in the picture. Some pubs still do. What’s the story? As a regular customer of the pub, you could become a member of the ‘savings-club’. You got your number, and every time you felt like saving some money, you put it into the narrow slit under your number. The management of the club, which was most of the time the pub-owner assisted by two members of the club, would open the cabinet every week. They took out the money, counted it and wrote it up under each member’s name, and brought the total sum to the bank to deposit it in a savings account
Once a year, all members got their money back plus the interest paid by the bank. This event was one of the high times of the pub, and it was celebrated with a big meal, dancing and plenty of beer. The brewer donated a free keg, and other merchants of the neighborhood donated gifts for a lottery. Most of the money saved during the year was in fact spent that same evening in the pub.
Such clubs made sense for the pub-owner. Little by little, the patrons saved money for the big coming event at their pub. Bank interest was earned, and that would also be spent at the pub. The more clubs choose the pub as their headquarters, the more regular patrons the pub had.

The “spaar-bak” in the picture can be seen at the Sincfala museum in Knokke-Heist (Belgium) where an early 20th century pub is recreated.
Newsletter May, 2001