X-Mark signature, also known as a cross-mark signature, is a type of signature used by individuals who are unable to sign their name due to illiteracy or physical disabilities. It involves the signer making a distinctive "X" mark on the signature line instead of their signature.

In legal and financial documents, an X-Mark signature is generally accepted as a valid form of signature, provided that the signer is able to demonstrate that they are the intended signatory and that they understand the nature and contents of the document they are signing. This can be done through various means, such as having the document read aloud to them and having them indicate their agreement, or having a witness present who can attest to the signer's identity and understanding.

However, in some cases, an X-Mark signature may not be accepted as a valid form of signature. This can happen if the document in question requires a specific form of signature, such as a notarized signature, or if the X-Mark signature is deemed to be illegible or fraudulent.

Overall, the use of X-Mark signatures is relatively rare in modern times, as most individuals are able to sign their name in a more traditional manner. However, for those who are unable to do so, X-Mark signatures remain a legally recognized and accepted form of signature in many jurisdictions.