how could i add digital signature to Forms?

Hi Nechama Hemed Havardi

Not with Forms alone at this time.

However it's possible that you could use Microsoft Flow to take the response, have an email sent the submitter with the details for approval (the verification would be that they have used their registration email to confirm what they have submitted), which will then trigger an email to you with the response.

You could also have the response stored in SharePoint, or as a document, etc (I have set something similar up in my company).

It's a workaround and the UserVoice idea below is a good one for proper functionality.

Cheers

Damien