Will depend on the actual configuration of the company. If You are directly issued the shares in the company (without referring to nominee shareholder service), then Share Certificate(s) is Your proof of ownership. If nominee shareholder is involved, then Your proof of beneficial ownership is confirmed by a different legal document, which can be a declaration of trust, a deed of transfer, a nominee services agreement, a beneficial owner declaration – regardless of the name, such document, signed by the nominee, would indicate in absolute certainty that You are the real owner of the company.