The advertisement appeared in the Berlin subway a few months ago. It reminded commuters that two deutschmarks was almost exactly equal to one euro using a witty punchline: "The euro will halve the number of German millionaires overnight".

But growing numbers of German millionaires are becoming more determined that they will still be millionaires in the new year, whatever the currency.

With only 32 days to €-Day, they have rounded up the undeclared cash they had hidden in their freezers, the favourite place for Germans to hide money, and toilet cisterns. Rather than wait for their marks to become worthless next year, they are emptying their mattresses and biscuit tins, and getting rid of their marks any way they can.

"For people with large amounts of undeclared cash there is a feeling of unmitigated panic," said Mr Dieter Ondracek, head of the German Tax Authority.

But what should Germans do with their ill-gotten gains? Already, record numbers are taking a chance and smuggling their money out of the country to banks in Liechtenstein or Austria. A private bank high in the Austrian Alps has deposits totalling DM1.64 billion (€0.84 billion), despite being situated in a town with only 370 inhabitants.

But not everyone has the time, or the nerves of steel, to make the trip. German millionaires not prepared to take the chance have realised they have to go from big hoarder to big spender, and quick. What they buy, whether life insurance or a yacht, isn't that important. It just has to be expensive.

The Bundesbank estimates that Germans hoarded around DM100 billion away from the taxman last year alone. Now, roving teams from the finance ministry are hoping to mop up at least some of that money by the end of the year.

For those with more than just a few hundred marks hidden in the toilet, why not buy a yacht? More than a few German have had the idea: exhibitors at boat shows around Germany say they have never sold as many boats as they have this year.

With that in mind, a 14-strong team of tax investigators raided the "Interboot" international boat show at Friedrichshafen near the Swiss border last September. Without warning, they pushed through the crowds milling around the yachts and approached the mainly foreign boat dealers.

"The officers visited a number of randomly chosen exhibitors of expensive yachts," said local tax official Mr Elmar Reichel, in an interview with Der Spiegel magazine. "We demanded to see sales contracts and offers that had been made." A number of people who bought new yachts will soon be getting unwelcome visits from the taxman, he said.

Of particular interest were people who deliberately bought expensive yachts with cash from a foreign company, thinking they had beaten the taxman.

"We got information from foreign exhibitors over which we usually would have no authority," said Mr Reichle.

Without much fuss, a yacht dealer from Liechtenstein handed over the names and addresses of 10 buyers.

The dirty-money spending spree in Germany is so well advanced that tax officials have categories for these new spendthrifts. There are the "worry savers", who started by putting something for a rainy day in behind the frozen meat and kept adding to it. They are most likely to try to spend their money on fur coats or property in Majorca. The group most likely to have "dirty money" are manual workers like plumbers and carpenters.

"Every second manual worker has dirty money," said Mr Hans Manteuffel, a Dⁿsseldorf-based lawyer. But it's not just these workers, he says. Anyone who writes their own bills for every transaction is suspect because they can then declare their gross earnings as net.

"I know a man who has a two-digit million sum hidden in his apartment," said Mr Manteuffel.

With so much dirty money floating around, it's not surprising that people are running out of things to buy; after all there are only so many yachts and fur coats you can purchase.

Many middle-aged Germans believe they have found the solution to their financial predicament over the border in Switzerland: life insurance policies, bought with one-off cash payments.

But border police will pass on your name to the taxman if you are caught travelling with DM30,000 (€15,300) or more, so the Swiss insurance companies have come to Germany for clients. One Swiss insurance agent says he has covered more than 4,000 km in recent months visiting his varied clientele around Germany.

Pharmacists, doctors, businessmen and, even once, a nice old woman have invited him for coffee and cake. They all had one thing in common: money to hide. The Swiss agent will call to their house, advise them on what policy is best suited to their needs, and will sometimes even collect the money personally and deliver it to the insurance company in Zⁿrich.

"With some customers I have to pick up the money in the middle of the night. At times I have had over DM150,000 in the car," said Mr Peter S. to Der Spiegel. He says trade has picked up significantly in recent months because insurance policies are the perfect tax dodge.

A customer signs a power of attorney giving an insurance agent control over the money. The agent transfers the money to a Swiss life insurance company as a one-off payment on behalf of the customer. After 12 years, the policy is tax-free and the customer can then cash it in.

"I wouldn't rule it out, that life insurance policies are being used to avoid paying tax," said Mr Michael Thelen, a tax investigator in Hamburg. The phenomenon is not new to tax investigators, nor to the federal government, but little can be done to stop the exodus of marks ahead of €-Day.

Insurance companies in Switzerland know that even large cash payments for insurance policies are generally not covered by money-laundering laws, even if the payments involve tax evasion. Last year, customs officers discovered more than DM100 million in cash bound for Switzerland. By mid-August of this year, customs officers had surpassed that haul and know this is only scratching the surface of money bound for Swiss banks and insurance companies.

But while German border police search cars, Switzerland says it has no intention of stepping up its own border patrols. Mr Hermann Kaestli, from the Swiss Customs Office, says suspected money smuggling is only investigated in the banks and not so much at border crossings.

"In exceptional cases where customs officials come across large sums of money, they can call in the police to investigate the matter there and then," said Mr Kaestli. But this rarely happens in the case of insurance scams.

Considering that the two Swiss authorities charged with investigating money laundering are chronically underfunded and understaffed, the risk is even smaller.

German retailer Saturn has been doing its bit to cash in on the trend, with adverts targeted at those who still have dirty money to spare. "Oh you joyous dirty money season," shouted a recent advertisement. In a tongue-in-cheek sales ploy, they advertised an expensive home cinema system by telling their customers that "getting rid of your dirty money has never been such great value".