A rather humorous little sketch, so simple, yet so effective.
Very often there is a face peering into the picture, as if they wonder what was going on, and staring at the viewer.
This sketch was done using felt tip, which Lowry often used.
The only trouble with felt tip, is that it fades, and in the 1960s and 1970s there was no special glass to block the UV light..
at least not generally available to the public.
Nowadays we can easily protect such works with UV blocking glass.