Smoking in public places in Wales has become illegal ahead of the English ban in July.
Any smokers caught lighting up now face a £50 fine and the Assembly Government has embarked on an advertising and publicity campaign to warn people about the ban.
English smokers will not have to stub out their cigarettes until July 1 and a backbench bid to delay the Welsh ban and bring both sides of the border into line was defeated in the Assembly earlier this year.
Ministers say the three smoke-free months could save 100 lives as passive smoking kills 400 people a year in Wales.
Wales was the first part of the UK to call for a ban, but because of the Assembly's limited law-making powers it had to wait until Parliament passed legislation last year.
Landlords and managers who do not display adequate no-smoking signs will be fined £200. They will face a fine of up to £2,500 if they allow people to smoke on their premises.
Anyone issued with a penalty notice can challenge it in court in the same way as a speeding ticket.
Health minister Brian Gibbons said: "I would be shocked if there is anybody who this is likely to affect in Wales who doesn't know that the ban is coming in."
The Scottish Executive heralded its year-old ban as a success last week when it said there had been more than 46,000 attempts to quit smoking since it began.