Martin eliminated the "mustache", which is really called a parend, at the base of the instrument in 1950. Yours is post-1950.
Martin eliminated the fretboard "stripe" and used the seven dot pattern in 1955, if this is true of yours (and I think it is from the photo), yours is post 1955.
Finally, Martin added Made In USA in the sound hole in 1960. If yours does not have this, then
yours is 1955-1960, specifically.
(If yours does have this Made In America, and I can't see it in the photo, it is post-1960).
I'm not a Martin savante, and I'm not even a Chris Tarman; all here is according to Walsh/King.
I think, but do not know, that Remco ('zaza) is playing that vintage Martin 3 in this fabulous video (while the uke vintage could be challenged, the fabulousness of the video is without repute).
http://www.youtube.com/watch?v=bQxOV9AFC5g
Why do I guess 1955-60 style 3 and not a style 2 for Remco? The seven fretboard dot pattern. Again, a guess. I think they are lovely, and do reflect a time of cost cutting for Martin, who essentially emasculated the Martin 3 style to save some hand work, but, thankfully, later reinstated the parend and striped fretboard in the latest models. (that very last line is opinion only). Yours, or the one pictured, is in stunning condition, cigar. A worthy part of a Martin 3 serial collection. Thank you for sharing it. There is one like it on eBay now, same vintage (I emailed the seller that his dates are wrong, but he didn;t change the listing) but he's asking an arm and a leg for it. It's only worth an arm.