Being retired from UK Government Service, I used to sign for fellow Brits and none was ever declined. However, a month ago when mine arrived at our new address, I noticed some significant changes from previous forms and having only lived in this isolated area for 18 months, I didn't know who ask. So off to my ttb bank where they instantly refused point blank even though I've had the account for 20 years.
Right out of the blue, my missus suggested driving 65km to Roi Et Immigration where they willingly obliged, naturally, for a small donation. The Officer concerned was a Lieutenant Colonel no less so it should be OK.
I have information they are tightening up on these forms so signing your own may cause future problems.
18 months ago a 74 year old friend of mine received his first as he had never told them he was here. Wrong advice from the wrong person who said they would never find out -- until they stopped his pension. The guy is now back in Blighty living in a Salvation Army Hostel or similar trying to pay back 7 years of over payments.