Smoking

There was at least one season sponsored by a tobacco company, and the actors were "urged" (compelled?) to smoke as much as possible. Of course, William Hopper was a heavy smoker, and needed no encouragement. (Oddly, he died of a stroke, not lung cancer.)

It's perfectly legal for characters in TV shows to smoke. But it's never been particularly common, because (in my view) it creates continuity problems when shooting a scene from different angles/distances.

The important Surgeon General's report that linked smoking and cancer came out in 1965, IIRC. By the late '60s cigarette advertising was prohibited on television and radio. Also by then a lot of the media stars of the 30s and 40s were dying of lung cancer and other lung disorders. I don't know if it was ever forbidden to smoke on a tv show as much as it just became very unpopular, and maybe the networks/shows weren't pressured by tobacco sponsors to show smoking.

Per the other response, a tobacco company was a sponsor during the second season; Burr said that it seems smoking was written into the script in about every scene. (per the Perry Mason TV Book.)

Having been a PM fan since the series had its first run through all the reruns, watching it again now the smoking of all the actors from Raymond Burr on down is what stands out for me. He even had a lighter prominently displayed on his desk!What is sadder is that Collins,Hopper and Talman all succumbed to smoking related illnesses and many of the guest stars.

Cigarettes were used as props in movies long before the introduction of network TV. For some actors holding ciggies put them in a comfort zone, giving their hands something to do while they said their lines.

William Hopper was one of those actors who needed a cigarette to hold according to the "Alliteratve Attorney " (book on PM).

After commercials were banned I believe it was ok to smoke in a show but discouraged. If the character was a known smoker, such as FDR, an actor playing him would smoke, or if it was written in the script that a fictitious character smoked. Cigars and pipes seemed to show up on shows often unlit. I remember Fred Flintstone did commercials for Winston cigarettes I was 6 years old and had candy cigarettes. Yabba Dabba Doo!

The guy that played BURGER did anti smoking ads later on...they're on youtube

in the 1950's and 60's there were lots of people smoking, even my non smoking parents kept ash trays in their home to be good host.
So in TV dramas in the 50's and 60's , it would be very normal for smoking to be done