The legality of XX signature has been witnessed and confirmed.

Example:

Seen for legalization of the signature and seal given by xxx.

The legalization of XXX’s signature and seal is confirmed from the date of witnessing.

Please note: This is a standard clause, meaning that the original document was submitted to the official who legalized the signature (and was therefore "seen" by him or her). It may have been "seen" by a notary, consul or other official.