Is it as easy as simply putting a sign in the window?

A friend of mine, who owns another rental site in a different country, has typically done very well because the vacancy rate where he is is so high (almost 10%). I think it’s actually even higher than that. So, naturally, property managers and landlords need to advertise more, and thus, more money being spent on advertising.
He has also said that if the vacancy rate is very low (like in many areas of Canada), that landlords and property managers only have to put a sign in the window of the rental for a day to rent it out. Sounds like pretty good logic.
I know that the vacancy rate, especially in the western provinces of Canada is very low….sometimes close to 1 or 2 %. I don’t personally live in those areas, but I’d be interested to find out from property managers living there if it is, in fact, that simple – putting a “For Rent” sign in the window to rent out a property, and if vacancy rate is the main variable that determines how much they spend in advertising and online listings.