Legal Question in Real Estate Law in California

In appropriate cases, the court can order the clerk of the court to sign (for example if signing the document is ordered as part of a family law judgment and the party refuses to sign).

But if the document is unrelated to the lawsuit the attorney represents the client on, I would doubt the attorney's signature has any legal effect as that is a subject matter the attorney does not represent him on.

Perhaps.....the court has inherent power to make such orders when appropriate, and while I think it would be quite unusual for it to order an attorney to sign another person's name to a deed of trust, it's conceivable. Judges often have their clerks sign a party's name to a deed or other instrument when the party, despite being ordered to do a certain transaction, refuses to do so. A frequent example is in dissolution of marriage cases where the spouses agree on a property settlement, but then one gets cold feet and refuses to deed the house over to the other. The court can order the clerk to sign the recalcitrant spouse's name on a deed.