If traveling abroad and using a credit card, always call your credit card company. Inform them where and when you will be traveling. Credit card companies are monitoring your credit card use. They have systems in place to flag your card for any unusual purchases for your protection.
For example, you live in Hawaii and you're in the Orient for a vacation and decide to do most of your shopping for gifts at one shop. You charge it on your VISA. The next day, you pay for lunch with the same card. The waiter returns and informs you that your card is not valid. You call the credit card company and realize they have placed your card on hold because of the unusual large amount charged outside of your country of residency. Once you inform them you are abroad, the card company will release the hold.
However the credit card company should be contacting you first before placing your card on hold. They will verify two things. First, that the card is in your possession. Second, that you authorized the transactions. If you have not contacted your card company first and you are already abroad, the card company has no idea where you are and therefore no way to contact you. They have no choice but to place the card on hold to prevent any fraudulent charges.
You probably never noticed, but If you look on the back of your credit card there should be a long-distance number to call when traveling abroad since the toll-free number can only be used while in the U.S. Believe it or not, you can call the card company collect when having problems with your card abroad. The card company should accept your call. The Hopeful Traveler speaks from experience.
Some card companies are already on the lookout before you leave home and not just for foreign charges. Before leaving Hawaii, The Hopeful Traveler once charged several different attractions with a company in New York City. The card company called me soon afterwards to verify the charges are valid.
One last thing. Be sure your credit card has your signature. Though credit card companies don't authorize this, some suggest that you write "ask for identification" in lieu of a signature. This flags the merchant to verify it is you making the charges and helps if you lose the card. This may give you some trouble if the merchant does not speak or read English well.
There will still be instances where you cannot help those merchants that just swipe the card without verifying the signature or identifcation of the patron. Of course, you may be the few who have a card with your photograph. This definitely helps in avoiding fraudulent charges.