I immediately thought of the picture in Stone, too. It is such an odd-ball among the other ones he pictures. One thought I had was to contact the Met and ask what they have on that particular sword. As I understand it, most (or all) of Stone's personal collection is there, so that dha might be as well. Of course, Stone was not always right in his attributions.
The blades look like long versions of a type of SEA utility knife (like the one Avner had at Timonium). They were discussed in another thread that I will find in a minute.
*Found it: http://www.vikingsword.com/vb/showthread.php?t=2067
; the knives are called "meed hnep." Looking at the pair again, it looks to me that the top one in the first picture definitely has a long tail, while the lower one appears to have a short tail. Also, the top has a distinctly curved beak, while the lower is more-or-less straight. So, they might represent different birds - the top a peacock and the bottom a crane. Finally, this would not be the first dha I have seen with a downwardly curved blade and handle:
This one is Burmese, supporting the peacock theory, and there are is one, also in an Oldman catalogue, classified as Burmese, a picture of which I am adding below.*
As for peacock versus heron, the shape of the heads looks more crane-like, with the long beak and bulbous forhead, but I checke out some pictures of peacocks on the net, and its not too much of a stretch. The bodies carved into the scabbard, however, could easily be those of peacock.
(scroll down to the second picture on the right side).
The thing about the peacock is that it is the national symbol of Burma, and of the old monarchy, so there would be more significance to a peacock than to a crane, at least in Burmese culture. I am not aware of either being of any particular significance in either Siamese or Lao culture.