Next time, please use the search and follow the community guidelines. There are already posts requesting this field type.

https://community.airtable.com/search?q=signature

If you just need form users to upload their signatures as attachments, you can use our extension. It allows you to collect hand signatures after form submissions.

Take a look at Plumsail Forms for Airtable. They offer a free plan and let you add signature fields, which save signatures as images directly in Airtable.