The IRS suggest care with this key number. Show your Social Security card to your employer when you start a job, the IRS says. Also show it to your financial institution for tax reporting purposes.
But in general, the IRS says you shouldn’t carry your Social Security card with you. For that matter, don’t carry other documents that display your number either. If your Social Security number is stolen, the IRS warns that someone else may use it to get a job. The unwitting employer may report the income to the IRS under your purloined Social Security number.
The IRS will assume when it sees that income reported to your number that you failed to report all your income on your tax return. Trouble will ensue. If you end up in this pickle, you can explain the fraud to the IRS and get our record updated. But you don’t want to go through this if you can help it. Be careful out there.
It has been my observation when in the US, people generally write a check more readily than using a debit card for such mundane purchases as groceries, etc., and it is common practice that their US social security number is inlcuded on their check. Boggles the mind.