An interesting question

[NickLangley]

Not strictly about insignia but related. A couple of days ago i was chatting to a friend who is a vintage bus enthusiast and he asked why it was that, back in the day, boroughs and cities would paint their buses and trams in distinctive liveries complete with the municipal coat of arms; their fire engines would have the brigade's name on the side in fancy goldleaf. But, when it came to their police forces municipal pride vanished and it was plain black for everyone. I didn't have an answer, but there must be a reason Does anyone know or have a theory?

Edited July 12, 2020 by NickLangley
style

[peter monahan]

Not as proud of their coppers?  After all, a large police force might be taken to imply a large criminal element in the Borough of Middle Wapping on Stokes on Trent.  Or, perhaps, they wanted a little discretion.  I'm guessing that black was the default colour for cars in the period you refer to.

[Tony Farrell]

It was simply the default paint finish. Bright colours on vehicles were generally not fashionable in the '50s and '60s (in the UK at least), which might be why white became the default police vehicle livery from the late '60s, as they needed to be more visible due to the increase in traffic and motorways.

The high-vis stripes were a '70s innovation to make them stand out even more as tastes changed - the high-vis aspect migrating over to ambulances, which were also corporately finished in whites, maroons and creams. Black was retained for some time on police vans, however, as it made them less conspicuous for scenarios that required their usage.

Buses? Deregulation sounded the death knell for classy corporation liveries and shepherded in the era of gaudy, decal-encrusted rubbish we still have today.