In an interview with mass-circulation daily Bild, the EU's Energy Commissioner was asked what Europe could do to provide an effective deterrent to breaking deficit rules, amid a crippling debt crisis.
Oettinger proposed that EU countries submit their budgets to the EU in advance for checking, then added: "We could also consider unconventional ideas."
The commissioner said: "There is also the suggestion that the flags of deficit sinners could be placed at half mast outside EU buildings. That would only be a symbol, but it would be a powerful deterrent."
Oettinger also proposed that the EU send "qualified officials" from other member states to help Greece with its administration.
However, he rejected the idea that debt-wracked Greece should be forced to leave the eurozone.
"That would divide Europe and would be a disastrous signal. It would give the impression that the EU is not in a position to stabilize a relatively small country," he said. "Markets and creditors would lose their trust in us in the future."