Wis. Stat. § 409.314: Perfection by control.

(1) Perfection by control. A security interest in investment property, deposit accounts, letter-of-credit rights, electronic chattel paper, or electronic documents may be perfected by control of the collateral under s. 407.106, 409.104, 409.105, 409.106, or 409.107.

(2) Specified collateral: time of perfection by control; continuation of perfection. A security interest in deposit accounts, electronic chattel paper, letter-of-credit rights, or electronic documents is perfected by control under s. 407.106, 409.104, 409.105, or 409.107 when the secured party obtains control and remains perfected by control only while the secured party retains control.

(3) Investment property: time of perfection by control; continuation of perfection. A security interest in investment property is perfected by control under s. 409.106 from the time the secured party obtains control and remains perfected by control until:

(a) The secured party does not have control; and

(b) One of the following occurs:

1. If the collateral is a certificated security, the debtor has or acquires possession of the security certificate;

2. If the collateral is an uncertificated security, the issuer has registered or registers the debtor as the registered owner; or

3. If the collateral is a security entitlement, the debtor is or becomes the entitlement holder.