Same for us. We’re only a small commune so the mayor’s secretary seems to know everyone. Took the form with our passports. She wrote passport details on form and told us to come back next day when the mayor would have signed them and put official stamp on. No problem.
If you mean the state pension; a retired police or fire officer (and presumably an armed services officer )can sign (giving their last headquarters details) - I confirmed this with the Pensions Service, as I have always signed for my ex-police neighbour , and he for me .
Mine does as well and it is mentioned on the form that a Pharmacist is acceptable. My problem is getting it back to the U.K. in the Poste. Have to send it the equivalent of reply and it is not cheap. One year it got lost ordinary post and my pension got stopped for 2 moths.
We send ours Recommandé avec avis de reception - That way we can track them and, as on one occasion, tell the DWP, what day they received it and by whom (with some deciphering of the signature). very expensive at 5.50 euros.