When my proof of life form came to me here I had to get signed and with a official stamp.
I went to Pattaya beach road police station where there is a officer who is assigned to do this and paid 200 baht plus a tip.
He duly completed the relevant section on the form in English and plonked the official Thai police stamp under his signature.
Lawyers, doctors etc can also do this if you can find one.
DWP send out the proof of life forms at random to your official address you registered with them, there is a time limit for you to respond, no response and your pension payments are stopped.