Snob screen

A snob screen is a device found in some British public houses of the Victorian era. Usually installed in sets, they comprise an etched glass pane in a movable wooden frame and were intended to allow middle class drinkers to see working class drinkers in an adjacent bar, but not to be seen by them, and to be undisturbed by the bar staff.

Pubs with surviving snob screens include:

...
Wikipedia