Since the 1934 version, the black ink on the front of the US dollar contains iron oxide, but different versions have different contents and different magnetic signal intensities, which can be detected by a good magnetic tester.

The US dollar is issued by the Federal Reserve, and there are 12 kinds of local Fed issues, which are represented by 12 letters respectively.

The letters of the old dollar (small front page) are in the middle of the bank seal.

Later versions cancelled the old bank seal and replaced it with letters printed on four rounded corners.

A under the 2003 series indicates that the signature of the US Treasury Secretary and other figures on the face have been changed in the series version. If the finance minister or the signature of the finance minister on the front of the US dollar is changed, letters will be added under the sequence, where A means one signature is changed and B means two signatures are changed.

In addition to magnetic induction and fiber yarn, the latest version of the dollar also has anti-counterfeiting measures such as watermark, color-changing ink, pearlescent ink, fluorescent ink, miniature letters, concentric patterns and anti-copying ink. This is a beautiful work of art. ..