Ron, the very early ones had bigger numbers engraved and no T on the dial, also dial surface finish and logo stand can be slightly different, what I have learned from my Heuer specialist: H tried to improve waterprove and used different tubes and slightly enlarged crowns during mid life cycle on some models, more to come on a special, 18 K always signed crowns, rest as Mark said...
Cheers Arno

: Hi guys, was enjoying my 2447N Carrera on my wrist today and
: started wondering from when the 2447s started having a signed
: crown. Most of us know that the Carrera Datos came without. They
: however have a Landeron 189 engine inside, while the 2447 came
: with a V72.

: Does anybody know. My 2447s serial number is 53865, maybe that's a
: clue. Or did they all come with a signed crown since 1962-1963?

: Greetings
: Ron