I came across a British term in grad school for a cannon traditionally fired in colonial India to signal the time of day when it became socially acceptable to drink alcohol. I emailed my old professor, but she's at a loss.
I possibly recall the term itself including the time of day (e.g. The Evening Gun, The 11'Oclock Blast) or a reference to alcohol (e.g. The Gin Cannon, Booze Boom..nah jk). There is a precedent for gun times in the British Empire, such as the Noon Cannon in Halifax, so I'm pretty sure I'm not imagining this.
Any referrals to similar practices in other cultures are also welcome.
Could the term you came across be the “Tiffin Gun”? It doesn’t refer to drinking directly. In colonial India tiffin referred to a light midday meal so the term, “the tiffin gun has gone” would by inference mean that it is after midday, by comparison with the well known noon cannons or noon guns in Hong Kong, Cape Town and, as you mentioned, Vancouver. I don’t know of any actual regular noon guns in British India.
The expression has similar meaning to the British Navy phrase “the sun is over the fore yard” or, more commonly, “the sun is over the yard arm” which literally mean that the time is about midday but are used to mean that it is now an acceptable time to drink.
Tiffin gun is not a common phrase but Evelyn Waugh used it in a novel in 1934 when a character comically attempts to buy a tiffin gun to go hunting. In context, Waugh obviously expects his readers to be familiar with the phrase.
In the Middle East, the Muslim festival of Ramadan has a similar occurrence. During ramadan, Muslims fast during the day, but are allowed to eat after sunset. At sunset, in most Muslim communities (I have encountered it in East Jerusalem) a cannon is fired to signal the end of the fast and the beginning of the Iftar, the Ramadan evening meal.
It does not appear to be mandated in holy texts, but is rather the result of a tradition stemming from a time before watches and clocks were common, but a specific time of day needed to be announced to an entire city, according to this news article. The article states that the tradition started in the Mameluke period (right before the beginning of the Ottoman Empire).
Therefore cannons were certainly used for signalling, though I am not familiar with the specific signal tradition to which you are referring, though it could be an adaptation of the Ramadan cannon, given the history of Islam in early India.