Had a Model 59 with the adjustable sight or had an adjustable sight? The latter weren't all that uncommon, but depending on your definition of "special" , maybe so. About 4 years ago a member here on the forum when provided one for me when I upgraded the Model 39-2 I had inherited from my Dad. I'm not sure they were ever available factory installed (perhaps as a special order option?)
I have to admit to being fairly new to this subset of S&W and finding out new stuff about the 1st-3rd Generation autos from just about every thread that shows up here. Perhaps someone will come along and tell us the code to look for on the end label of a box that came with an adjustable sighted 39 or 59.
Froggie