I was wondering where should the Captain sign in the logbook?
Anywhere in the column should be sufficient, the easiest way is just to write it into the remarks section though.
as the CAA want a letter from my company saying how many hours I have flown on PIC(US) what should such a letter contain
You shouldn't need both the Captains signatures and a letter, its usually just one or the other.
Basically the letter must say something like:
Dear Sir
I can confirm that [Your Name] has recorded [the hours you are claiming] P1u/s hours, I have checked these hours personally and confirm they are correct.
Sincerely
[Chief Pilot/CEO/Head of Training etc]
The important point is the actual P1u/s hours you are claiming MUST be written onto the letter as a number so the have an official document in their records.
