credit card trivia

So I've only been using credit cards for what - 30 years? I thought I knew everything, but found a few gems I didn't know on consumerist.com:

1. Unsigned cards are not valid and merchants can and will refuse them
2. The maximum liability for unauthorized use of a credit card (not Debit/ATM cards) is US$50 according to federal law
3. Merchants cannot require you to present ID, unless your card is unsigned
4. Merchants cannot require a minimum transaction amount
5. Merchants cannot charge a surcharge for using a credit card, however, they can offer a cash discount
6. Many credit cards have programs that will automatically double the manufacturer's warranty and other excellent benefits
7. Merchants are not allowed to make you give up your right to a chargeback
8. Merchants are not allowed to place a hold for the estimated tip
9. If merchants suspect you of fraud they are supposed to call with a "Code 10"
10. If merchants break these rules, you can report them to the credit card company

Full article: 10 Things You Might Not Know About Your Credit Card