A section of a Wikipedia article that might be of interest:
https://en.wikipedia.org/wiki/Barefoot#Imprisonment_and_slavery

Removing the footwear and making a captive go barefoot has been one of the first conventional methods to tag and identify prisoners in most civilizations. It was a usual feature and often the principle element of early prison uniforms. The visual aspect of bare feet is therefore used to contrast the conventional appearance as footwear is regarded an obligatory clothing feature in urbanized cultures.

Besides the indicatory aspect going in bare feet restricts the freedom of action in many situations. A barefooted person is therefore disadvantaged opposite a shod person in many practical respects. This aspect is often used to exercise physical control over individuals in captivity.

A barefoot person is usually disadvantaged in a physical confrontation against shod individuals. Drastically more severe injuries can be sustained especially by a kicking person outfitted with footwear in contrast to a person in bare feet. For this reason shoes are considered deadly weapons by penal laws of most countries. Bare feet on the other hand present an opportune and vulnerable target for the application of force. These effects are usually desired by correctional or police officers primarily in confrontational situations with antagonistic individuals. The risk of personal injury is therefore notably reduced and the situation can often be resolved more efficiently.

Another main objective is preventing and counteracting potential attempts of prison escape. Without the protection of the feet that shoes standardly provide, the locomotion of an unshod person is more difficult in the majority of exterior environments, so a potential fugitive is easier to retrieve in many cases. Detainees are often discouraged from attempting escape by this measure alone.[31]

A barefoot person experiences certain discomfort in daily life situations. The desire to be protected from the common inconveniences of the ground, mostly due to coarse textures or adverse temperatures, prompted humans to make use of footwear in ancient history. Incidentally the traditional visual appearance of civilized societies was established, including footwear as an obligatory feature. A forced exclusion from the conveniences and also appearance of footwear typically creates an frequent awareness of being vulnerable, therefore it can have an intimidating effect on a person. The enforcement of bare feet often creates a consciousness of being powerless and degraded notably on prisoners, as they typically cannot relieve this situation on their own.[32]

As the practical effects are typically achieved effortlessly, keeping captives or prisoners barefoot has been cross-culturally practiced since antiquity.[33]

It was also commonly practiced to identify slaves in former times.

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