New Expert here.
"A client can authorize an attorney to perform those ministerial acts necessary to conclude a settlement. (Palomo v. State Bar (1984) 36 Cal.3d 785, 794 [205 Cal.Rptr. 834] [client can expressly authorize attorney to endorse client’s name to a settlement check]; Matter of Lazarus (Review Dept. 1991) 1 Cal. Bar Ct. Rptr. 387, 396-97 [permissible for a client to expressly authorize an attorney to sign a client’s name on documents related to the client’s case].)"
Palomo v. State Bar (1984) 36 Cal.3d 785 states at page 793-795:
" The hearing panel found, among other things, that petitioner had endorsed his client's signature to the estate distribution check without Torres' knowledge or consent.  An attorney who does so engages in serious misconduct. (E.g., Silver v. State Bar (1974) 13 Cal.3d 134, 144 [117 Cal.Rptr. 821, 528 P.2d 1157]; Himmel v. State Bar (1971) 4 Cal.3d 786, 798 [94 Cal.Rptr. 825, 484 P.2d 993].) [5b] Petitioner concedes he had no express authority from Torres, but he contends the broad power of attorney contained in the retainer agreement permitted him to endorse the check. We disagree."
"Our past disciplinary cases have assumed that representational authority alone does not constitute the client's consent to simulation of his signature on a draft payable in his name. (Silver, supra, 13 Cal.3d at p. 144; Himmel, supra, 4 Cal.3d at p. 798.) fn. 5 [5c] Since it is undisputed that Torres gave no actual consent to petitioner's endorsement, the finding of misconduct is valid. fn. 6
If the lawyer did not have written authorization to sign the client's name, it was misconduct to have done that.
I hope this information is helpful.