I wonder if they were giving their full official seal? I suppose if you're signing a ton of documents, handing that over might be needed. It would be interesting if there were a system to register certain seals with only some permissions (for example, manage business but not personal assets with a green seal). You could create a document stamped with your most important seal that indicates which seal is permissible for which purpose.
In Japan, the official "hanko" seal with red ink carries the force of a signature, but other seals do not carry as much or any legal weight.
https://www.nippon.com/en/features/jg00077/
That article talks a little bit about a similar system to the one I mentioned, where one seal is used for banking, one for title transactions, etc. Something like that but more customizable could be pretty useful.